Themes: Handle apps using "original-package" tag

Before this patch the themes code assumed the pkgName from PackageInfo was equal to the
manifest value. This is not the case however for upgraded system apps that have gone
through a pkg-name change. For example, Trebuchet was "com.android.launcher3" and now
it is "com.cyanogenmod.trebuchet". If the device had wiped data then PM would use the new
pkg-name, but if the system apps were being upgraded then PM would use the old name which is
now different from the manifest name.

Change-Id: Ie7eb1b4e17899d1055535dc890d4f7a7bca9a98a