retain / release & static map for opengl objects could be abstracted

[ofZach]

in reviewing the code, we've seen a bunch of chunks of code for each opengl based object that handles a static map between GLunits and int ids, and which has retain and release code that the objects (ofLight, ofTexture, ofFbo) use. It seems like this code could be written once (glManager?), and then used in multiple places, with some minor customization based on the object you're tracking. It would mean less repetition in the code, and if we want to expand on what this code does it will make it easier to have it only in one place.

[arturoc]

i was thinking that we could move to smartpointers or add a glResourceManager that takes care of this or both, the destructor for the gl resources actually tells the glResourceManger to destroy that resource in the next update so it happens in the correct thread no matter where the destruction of the actual object happens