CM11 Themes: Common overlay for sharing resources. [1/2]

This patch will allow themes to contain common resources
which can be shared by all overlays.

Common resources will reside in assets/overlays/common and
can be referenced by other overlays.

Common resources will be referenced using the common package
name, i.e. To reference the common drawable some_drawable for
com.example.theme the theme designer would use
"@*common:drawable/some_drawable"

Change-Id: I395b6bd5eae91b00265a8e9221856ef7bf5d115a
Revert 'Theme engine: Support launcher based icon packs'

Before this patch, icon packs written for Trebuchet/Nova/Apex could not be used
with the new theme engine as the formats were different. Particularly the icon package IDs are 7F,
the same ID as as regular apps. Furthermore the location of resources in these icon packs was different
from what the theme engine expects. This patch adds support for these icon packs by overriding
the pkg id.

AssetManager now can override package ids without requiring aapt to recompile the APK.
Note: XML references will still use the original id compiled with AAPT, so it is only useful for resources
which do not use xml drawables (such as icon packs).

PackageInfo now has a new member identify "legacy" (3rd party icon packs) written
for launcher's like Trebuchet, Nova, and Apex.

Change-Id: Icd12c097e156c9626df0772abeb50e00f7b61f64 (reverted from commit e021b28eaef6580e224e89a783e7933f14a69382)