CM11 Themes: Use package name from AndroidManifest

It is possible for an apk to have a different package
name for the resources than what is defined in the
AndroidManifest.xml of the apk.  Using the resource's
package name for the base package name causes themed
resources to not be properly loaded.

Instead of returning the resource package name we return
the apps package name from AssetManager.

A good example of this is Trebuchet.  The system sees
it as com.cyanogenmod.trebuchet but it's resources use
com.android.launcher3.

Change-Id: Id57e68b27b3c7509e3358a7fd12ae73a03dd6cdf