fb: Show heads up at the bottom of the screen (1/2)

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.

As well this commit fixes the wrong gap on the top if user boots up directly
into immersive mode.

PS:
- if IME keyboard is showing show the heads up on the top to do not disturb the typing.
PS:
- NPE if updatePosition is called to early from the system.

Change-Id: Iea7fbe466808531a9351cf4048570b8f56eb698e

Conflicts:
	packages/Keyguard/res/values/custom_dimens.xml
	packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBar.java