Improving home screen customization

- Created a drawer with tabs for widgets, folders, shortcuts, wallpapers
(wallpapers are currently not implemented)
- Tapping outside the drawer dismisses it
- Moved the all apps icon to the upper right of the screen
- Adding a toast that says "No more space on screen" when dragging a widget to a full screen
- Fixed bug where you could stack two equal-sized widgets on top of each other on the homescreen (exposed by the new ability to drag widgets onto the home screen)

Change-Id: I03b65ce54a85d24328c94e0c06e249571de449ee
17 files changed