Adding Jank tests for watch face picker

The following test cases will be added:
1. Removing watch face from favorites.
2. Adding watch face from full list to favorites.
3. Fling on favorites list.
4. Fling on watch face full list.

In addition, there are few refactoring:
1. Modulerizing transitions between screens into method (step).
2. Introducing flingLeft() and flingRight() for flinging picker.

Change-Id: Idccb07548b1258bba451cbecdfb2b20a3e2afb55