Themes: Avoid compiling icon packs every boot

Change-Id: I51c7effdd4592a302f457822a05cbebee6cde06b
synchronize updateStringCache on mAccessLock

Resources.java used to synchronize on mTmpValue but has since
switched to mAccessLock. mTmpValue can be null in some instances
causing a NPE during a theme change.

Change-Id: I7411dfdf6e8e411381ae993872a3c740dad19300
sync status bar transparency state on theme change

When the status bar view is reinflated its transparency mode is
reset back to opaque. This can be observed by changing a theme
and switching to home in the middle of a switch.

Change-Id: I3049c5f24cc6c46dcefb24188039a08503db09a9