SystemUI: Allow theming battery via theme chooser

Change-Id: Iebea2dab0ed89baa14c0f18a4c8f487cdb8313a6
Merge "SystemUI: Allow theming battery via theme chooser" into cm-11.0
Revert "Fix a bootloop problem when /data/system/usagestats/usage-history.xml is empty. This often occurs after an incomplete reboot/shutdown or battery pull."

This reverts commit e290de5ecdd591d1978af1b0e9b3303696c849ed.

Change-Id: I5c30ef4560bed7c83243517ba8868069f2777613
Fix broken XML parsing idiom.

Code that expected a single top level element in an XML file
was doing something like :

while (type != START_TAG) { next(); }

This would loop forever when the XML being parsed was empty,
where each call to XmlPullParser.next() would return END_DOCUMENT.

bug: https://code.google.com/p/android/issues/detail?id=64173
Change-Id: I7543203e976a8999ae471a6c2d629249a87011bb
[WIP] Multi-window

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 :)

PS 11-16: Rebase

Change-Id: I4a03a84539fd3ac1273f0d3503fe8fafcd16be26