Implements PP shader system using attribute workaround.

This is pretty much a step backwards in our code. We used to use attributes in our PP shader system a long time ago but we changed it to attributeless
for code simplicity and cleanliness. This reimplements the attribute code path as an optional path to take in the case your system doesn't work with
attributeless rendering. In this case the only shipping drivers that we can know for sure supports attributeless rendering is the Nexus 5's v95 driver
that is included in the Android 5.0 image.

I hadn't planned on implementing a work around to get post processing working in these cases, but due to us force enabling the PP shader system at all
times it sort of went up on the priority list. We can't be having a supported platform black screening at all times can we?
This code will generates a new buffer on every shader update but only free the last one.