Animations for user switching.

The window manager now has a facility to provide a full-screen
animation, which the activity manager uses every time a user
switch happens.

The current animation is just a simple dumb slide until we get
a design from UX.

Also some cleanup: moved the portrait task animations to the
default config so we always have an animation for them, and finally
got the java symbol stuff out of public.xml.

Change-Id: I726f77422b2ef5f2d98f961f8da003e045f0ebe8