Importer: Full-screen viewing, UI refinement, refactoring

Bug: 7990333
Bug: 8151814
Bug: 8037411

This CL adds or changes the following things:
 - Full-screen image viewing and UI for switching modes
 - Moved general functionality from MtpThumbnailTileView
   to MtpImageView to allow for reuse in full-screen image
   use-case
 - MtpBitmapCache moved from ui to data package
 - Orientation now respected when set in image metadata
 - Miscellaneous UI consistency issues fixed
 - Miscellaneous instability issues fixed

Change-Id: I5f188b763617b693e32fedc03273d711d604922a
diff --git a/res/values/strings.xml b/res/values/strings.xml
index d6b9815..fae3466 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -503,6 +503,9 @@
     <!-- Label for album grid button -->
     <string name="switch_photo_grid">Grid view</string>
 
+    <!-- Label for fullscreen button. [CHAR LIMIT=20] -->
+    <string name="switch_photo_fullscreen">Fullscreen view</string>
+
     <!-- The tilte of a dialog showing trimming in progress. [CHAR LIMIT=20] -->
     <string name="trimming">Trimming</string>