Replace all ContextManager sharedInstance() usages with shared

Apart from being more Swift-y, this will also allow us to differentiate
between a shared instance for the Objective-C layer (`CoreDataStack`)
and one for the Swift layer (`CoreDataStackSwift`). This differentiation
will be valuable if/when we'll replace `ContextManager` references with
`CoreDataStack`/`CoreDataStackSwift` so that WordPressDataObjC can
refer to the functionality without knowing about `ContextManager`, which
is defined in the Swift WordPressData layer.

Author: mokagio

WordPress/Classes/Models/Blog/Blog+HomepageSettings.swift

@@ -106,7 +106,7 @@ extension Blog {
         guard let pageID = homepageType == .page ? homepagePageID
                 : homepageType == .posts ? homepagePostsPageID
                 : nil else { return nil }
-        let context = ContextManager.sharedInstance().mainContext
+        let context = ContextManager.shared.mainContext
         return lookupPost(withID: Int64(pageID), in: context) as? Page
     }
 }

WordPress/Classes/Models/Notifications/Actions/NotificationAction.swift

@@ -15,7 +15,7 @@ class DefaultNotificationActionCommand: FormattableContentActionCommand {
     }
 
     private(set) lazy var mainContext: NSManagedObjectContext? = {
-        return ContextManager.sharedInstance().mainContext
+        return ContextManager.shared.mainContext
     }()
 
     private(set) lazy var actionsService: NotificationActionsService? = {

WordPress/Classes/Services/AccountSettingsService.swift

@@ -64,7 +64,7 @@ class AccountSettingsService {
         self.init(userID: userID, remote: remote)
     }
 
-    init(userID: Int, remote: AccountSettingsRemoteInterface, coreDataStack: CoreDataStackSwift = ContextManager.sharedInstance()) {
+    init(userID: Int, remote: AccountSettingsRemoteInterface, coreDataStack: CoreDataStackSwift = ContextManager.shared) {
         self.userID = userID
         self.remote = remote
         self.coreDataStack = coreDataStack

WordPress/Classes/Services/JetpackNotificationMigrationService.swift

@@ -26,7 +26,7 @@ final class JetpackNotificationMigrationService: JetpackNotificationMigrationSer
     }
 
     private lazy var notificationSettingsService: NotificationSettingsService? = {
-        NotificationSettingsService(coreDataStack: ContextManager.sharedInstance())
+        NotificationSettingsService(coreDataStack: ContextManager.shared)
     }()
 
     private lazy var bloggingRemindersScheduler: BloggingRemindersScheduler? = {

WordPress/Classes/Services/NotificationSyncMediator.swift

@@ -79,7 +79,7 @@ final class NotificationSyncMediator: NotificationSyncMediatorProtocol {
     /// Designed Initializer
     ///
     convenience init?() {
-        let manager = ContextManager.sharedInstance()
+        let manager = ContextManager.shared
 
         guard let dotcomAPI = try? WPAccount.lookupDefaultWordPressComAccount(in: manager.mainContext)?.wordPressComRestApi else {
             return nil

WordPress/Classes/Services/PostCoordinator.swift

@@ -61,7 +61,7 @@ class PostCoordinator: NSObject {
 
     init(mediaCoordinator: MediaCoordinator? = nil,
          actionDispatcherFacade: ActionDispatcherFacade = ActionDispatcherFacade(),
-         coreDataStack: CoreDataStackSwift = ContextManager.sharedInstance()) {
+         coreDataStack: CoreDataStackSwift = ContextManager.shared) {
         self.coreDataStack = coreDataStack
         self.mediaCoordinator = mediaCoordinator ?? MediaCoordinator.shared
         self.actionDispatcherFacade = actionDispatcherFacade

WordPress/Classes/Services/PostService+Revisions.swift

@@ -23,7 +23,7 @@ extension PostService {
                                             for: postId.intValue,
                                             with: blogId.intValue
                                         )
-                                        ContextManager.sharedInstance().save(self.managedObjectContext, completion: success, on: .main)
+                                        ContextManager.shared.save(self.managedObjectContext, completion: success, on: .main)
                                     }
         }, failure: failure)
     }

WordPress/Classes/Services/PostService+UnattachedMedia.swift

@@ -15,7 +15,7 @@ extension PostService {
 
         let mediaService = MediaService(managedObjectContext: self.managedObjectContext)
         mediaService.updateMedia(mediaToUpdate, fieldsToUpdate: ["postID"], overallSuccess: {
-            ContextManager.sharedInstance().save(self.managedObjectContext)
+            ContextManager.shared.save(self.managedObjectContext)
             success()
         }) { error in
             failure(error)

WordPress/Classes/Services/WordPressComSyncService.swift

@@ -65,7 +65,7 @@ class WordPressComSyncService {
     ///   - onFailure: Failure block
     ///
     func syncOrAssociateBlogs(account: WPAccount, isJetpackLogin: Bool, onSuccess: @escaping (WPAccount) -> Void, onFailure: @escaping (Error) -> Void) {
-        let accountService = AccountService(coreDataStack: ContextManager.sharedInstance())
+        let accountService = AccountService(coreDataStack: ContextManager.shared)
 
         let onFailureInternal = { (error: Error) in
             /// At this point the user is authed and there is a valid account in core data. Make a note of the error and just dismiss

WordPress/Classes/Stores/ActivityStore.swift

@@ -100,7 +100,7 @@ class ActivityStore: QueryStore<ActivityStoreState, ActivityQuery> {
          activityServiceRemote: ActivityServiceRemote? = nil,
          backupService: JetpackBackupService? = nil) {
         self.activityServiceRemote = activityServiceRemote
-        self.backupService = backupService ?? JetpackBackupService(coreDataStack: ContextManager.sharedInstance())
+        self.backupService = backupService ?? JetpackBackupService(coreDataStack: ContextManager.shared)
         super.init(initialState: ActivityStoreState(), dispatcher: dispatcher)
     }