Turn animations on by default.

Add API to skip the animation for a particular start activity, so that
a latter better one can be used.

Fix Theme.NoDisplay to actually work.

Fiddle with various animations: don't do a different animation for task
switching, try a scale animation for switching in/out of the wallpaper.

Adjust the animation duration so that at normal speed we have something
more like the slower animation option (so slow is now the default).

Change-Id: Ieba9f3db0bd9a762a19b327a3ecccbc7b547893d