[WIP] Multi-window

change flags to work with HALO already
still buggy, need to play with the app priority issue.

This is a big work in progress, which currently has some bugs,
but begins to look okay.
You can already multitask a little bit, by using the
app switcher and long-pressing an icon, then select "Add to
Split View".
Last window touched gets the key focus.
Code is very ugly, I know. Don't merge it, don't use it
for now. Unless you want to make your code ugly.
Enjoy :)

Change-Id: I455627e5fe2d3c05d9762222372d339e6cae6de2

Conflicts:
	core/java/android/app/Activity.java
	core/java/android/inputmethodservice/InputMethodService.java
	core/java/android/view/IWindowManager.aidl
	packages/SystemUI/res/values/strings.xml
	packages/SystemUI/src/com/android/systemui/recent/RecentsPanelView.java
	services/java/com/android/server/wm/WindowManagerService.java