Base: Floating window with multitasking

basic floating window are taken from AOSPA (HALO) by @D4rKn3sSyS

Drawables courtesy of @Alex Cruz thanks to him :)

with heavy change to get this work for multitasking

this feature, has ability to:
1. Moveable window to various position
2. Scaling window with 2 finger like zoom in/out
3. Double tap in actionbar or above window to fullscreen or back to floating window
4. Automatically resize when Snapping into one of side (Top, Bottom, Left, Right)
   (taken from xhalofloatingwindow by @zst123)
5. Automatically switch focus from other app (taken from multiwindow by @xplodwild)
6. Unlimited floating window app (depends on RAM)

this is still under testing, to make fully works
so if there any bug because of this, DO NOT REPORT INTO OMNIROM JIRA

to make app launch using Floating window feature

you must add Intent.FLAG_FLOATING_WINDOW
before start an activity

for example you can look at https://gerrit.omnirom.org/6515

need https://gerrit.omnirom.org/#/c/6561

PS.17 : fix scaling
PS.18 : fix layout calculation when rotate
PS.19 : support minimize/maximize window (see App circle sidebar)
PS.20 : fix previouse app

Change-Id: Iad00c239de7d66e8bb45205ce626d4f08417b7cd

Conflicts:
	core/java/android/content/Intent.java
	core/res/res/values/custom_symbols.xml