Settings: Show heads up at the bottom of the screen (2/2)
Due of user requests and indeed especially on hw key devices for a better
workflow we add an option to show heads up notifications on the bottom instead
of the top.

Animation we leave as is due that if it slide from the bottom into the screen it happens
to often that the user accidentaly interacts with it. If it comes from the top of the
container we add, the user has enough time to realize it. Sometimes a ms can make a big difference.
Launch Heads Up in floating window [2/2]

AICP'fied.
PS2: Add another setting for testing
PS3: Add missing string
PS4: Remove test preference
Heads up: enable heads up notification checkbox for all

- Disbale check of system packages to allow checkbox for all. This will, for example, bring screenshot to heads up if SystemUI is enabled

Change-Id: I273caffa992e79a9a9d6914bf1c89f9388044da4