Some code clean-up in WindowManager.

- Renamed DisplayContent.findTaskForControlPoint to
DisplayContent.findTaskForResizePoint as it is trying to find a task
from the resize point.
- Renamed DisplayContent.checkForDeferredActions to
DisplayContent.onCompleteDeferredRemoval as the method removes containers
whose removal were deferred.
- Added methods TaskStack.hasMultipleTaskWithHomeTaskNotTop() and
topTaskIsOnTopLauncher()
- And some other minor clean-up relating to me trying to break-up a big CL.

Change-Id: I64d03cbd9ee69bf8fa0013a49283cd434b7c8fbe