settings: Various cleanups

 * Cleanup display settings ghetto:
   - Move Brightness to the top
   - Replace the single-option menu with a switch in cast screen
   - Create display category
   - Move Cast Screen to higher priority, move down Daydream and Font
   - Create advanced category
   - Relocate advanced stuff to the bottom, including DoubleTap to wake
 * Move gesture settings so it doesn't look like it's part of expanded
   desktop's category
 * Use a seekbar preference to allow setting arbitrary animation scale values

Todo (depend on outstanding draft patches) :

   - Remove Lockscreen wallpaper option from Lockscreen settings
       - Use new ThemeChooser instead
   - Kill Trebuchet sub-settings from Home settings

Change-Id: I4ceaf0dc74e6e044e36cf3652bfc1efb33890380