use local sdk source for the dev env

placed this in the settings.gradle file so this is defined next to where
the example app is being included.
This is done in this way so the example project can stay independent
and as close to a real world setup as possible.

Author: jkasten2

OneSignalSDK/settings.gradle

@@ -1,2 +1,14 @@
 include ':app', ':onesignal', ':unittest'
-project(':app').projectDir = new File(settingsDir, '../examples/OneSignalDemo/app')
+project(':app').projectDir = new File(settingsDir, '../examples/OneSignalDemo/app')
+
+// Allows running the :app project above with the local source for development of the SDK.
+// This means we can keep the example app as-is so it stays as a real world example.
+gradle.rootProject {
+    allprojects {
+        configurations.all {
+            resolutionStrategy.dependencySubstitution {
+                substitute(module('com.onesignal:OneSignal')).using(project(':onesignal'))
+            }
+        }
+    }
+}