"Clear all" button on recent apps

Port forward from cm-10.2

Change-Id: I9ebcf22f85957f61caefb14e0efd4cf2978d92cd
Add xxhdpi versions of our improved tethering icons

Change-Id: If943f81389774a1f8ca0407cab4756687a273be7
Merge "Add xxhdpi versions of our improved tethering icons" into cm-11.0
Merge remote-tracking branch 'upstream/cm-11.0' into HEAD