Add switch subspec, slider dependency to podspec

Summary:
This commit adds the subspec for MDCSwitch to the podspec. It also adds the
ThumbTrack as a dependency for MDCSlider as "pod lib lint" was complaining
about not being able to build the Slider due to it missing that header file.

Test Plan:
1. Run "pod lib lint --verbose --private material-components-ios.podspec"
2. Observe everything builds and there is only one warning

Reviewers: #material_components_ios_owners, junius

Reviewed By: #material_components_ios_owners, junius

Projects: #material_components_ios

Differential Revision: http://codereview.cc/D90

Author: traviskaufman

material-components-ios.podspec

@@ -78,6 +78,7 @@ Pod::Spec.new do |s|
     ss.public_header_files = 'components/Slider/src/*.h'
     ss.source_files = 'components/Slider/src/*.{h,m}', 'components/Slider/src/private/*.{h,m}'
     ss.header_mappings_dir = 'components/Slider/src/*'
+    ss.dependency 'material-components-ios/private/ThumbTrack'
   end
 
   s.subspec 'SpritedAnimationView' do |ss|
@@ -86,6 +87,16 @@ Pod::Spec.new do |s|
     ss.header_mappings_dir = 'components/SpritedAnimationView/src/*'
   end
 
+  s.subspec 'Switch' do |ss|
+    ss.public_header_files = 'components/Switch/src/*.h'
+    ss.source_files = 'components/Slider/src/*.{h,m}'
+    ss.header_mappings_dir = 'components/Switch/src/*'
+    ss.resource_bundles = {
+      'MaterialSwitch' => ['components/Switch/src/MaterialSwitch.bundle/*']
+    }
+    ss.dependency 'material-components-ios/private/ThumbTrack'
+  end
+
   s.subspec 'Typography' do |ss|
     ss.public_header_files = 'Typography/src/*.h'
     ss.source_files = 'Typography/src/*.{h,m}', 'Typography/src/Private/*.{h,m}'