On-The-Spot: Add Gif support

Now features can be explained in yummy animated goodness

GifView supports adding gifs programmatically or via xml using custom:gif=""

Change-Id: Ic1e383c11eb6b8a7a2200470fa31bb28dfc304f7
SystemUI: Do not use null value animators

This commit ensures that any null value animators that are
passed out from the transition generator are handled properly.

Relates to 'Make sure AnimatorSet avoids null animations'
(change id Icfd751b1abceccf7f1177680b86d30610471810e)

Change-Id: I04357e33cfe293c2a1329a7033a5acb53bfb5c85