Themes: Use first asset entry for lockscreen wallpaper

The current implementation assumes the wallpaper will be named
either wallpaper.png or wallpaper.jpg.  If this is not the case
the wallpaper is not applied.  This patch implements the lockscreen
wallpaper the same way that the regular wallpaper is done.

Change-Id: I9f3dd299c1e61158fa53c163f7e42e21e2f9b1dc
Themes: Use default_wallpaper for HOLO lockscreen wp

Change-Id: I9c7fd29c99d13e811993eb9b3b045010431ccad0
PackageManager: Add option for single threaded dexopt

* Execute all dexopt invocations on the main thread instead of using the
  ExecutorService when persist.sys.dalvik.multithread is set to false.

Change-Id: I3b8499d5af5091ad7abcddf006f8f2837943903b