Bug 951865 - Part 1: Replace ABI_DIR with ANDROID_CPU_ARCH. r=glandium
Bug 951865 - Part 2: Package GeckoView resources when building mobile/android/base. r=glandium

This is a temporary measure.  We have multiple resource directories
that all need to be included into the GeckoView library.  This patch
stuffs the resources into a zip file which can be included in the
GeckoView packaging step.

These resources used to be copied into res/, which led to
synchronization issues.  This new zip file will now suffer the same
synchronization problems.  Android Archive (.aar) files make this
synchronization step explicit, and tools such as gradle do the work to
keep things in sync.  We'll move to use a tool like this eventually,
but for now...