Bug 1106593: Proguard third-party libraries that ship with Fennec. r=nalexander

This applies Proguard to third-party libraries such as the Android
support-v4 library and the Google Play Services libraries.
Previously, these were not Proguarded, bloating the Fennec APK.

Technically, this required a few work-arounds, including:

* stripping library debug information with a early Proguard
  invocation;
* altering the optimizations tried; and
* reducing the number of Proguard passes.

--HG--
rename : mobile/android/config/proguard.cfg => mobile/android/config/proguard/proguard.cfg
extra : rebase_source : 6d638695b6c8f759578aba5f1eda668fc9c28e9d
extra : amend_source : 96a475c0739c4b44a3df3fdfd2c59321836d9694