Defer detach until animations are complete.

Allowing the detach of ActivityStack from DisplayContent to happen
immediately was causing all sorts of problems associated with not
having a Display to complete the animations.

Waiting for animations to complete before either the detach or the
display removal fixes those problems.

Change-Id: I8a5663bfac5c3c1084ff4fcc451e0e38e8080265
5 files changed