"Clear all" button on recent apps

Port forward from cm-10.2

Change-Id: I9ebcf22f85957f61caefb14e0efd4cf2978d92cd

Conflicts:
	packages/SystemUI/src/com/android/systemui/recent/RecentsHorizontalScrollView.java
Better close all recents button
Let us move the clear recent to the bottom corner for convenience.

Change-Id: I538af0e7d8d75985941e9542375211090d974df8