Let animations of insets controller can be disabled

In some cases, System UI needs to hide navigation bar without any
animation, i.e. transitioning to AOD. This CL creates a method in
insets controller to disable/enable animations.

Fix: 150729581
Test: Enable AOD, and go to AOD from home screen by pressing power key.
Test: Enter/leave bouncer while screen is on.
Change-Id: I3fb7be898b9e615c661d07eca97c9ffcb6bbf8c3