Hide overview and app icon split option when appropriate

Don't show app menu icon split option or overview
action split option when current taskView is already in
split or there are not at least 2 tasks with which to
invoke split

Fixes: 197245395
Test: Tested with small and large screen,
dismissing tasks in overview, with and without
GroupedTaskView as main running task

Change-Id: I90cc3c39e4d94662cb87314a210d45d145b6e026