Initial integration of abstract rendering

Abstract rendering framework integration working for count-based analysis.  Includes slots for aggregator, info, chains of shaders and a few basic shaders. 

Notes: 
* Requires separate installation of abstract rendering, but it prints an error if the import fails, including instructions for how to download/install from the main AR repo
* Axis ticks are wrong...just plain wrong.  Don't trust them when using AR.
* Merged in master at 2:46am on 13Jun2013.


Run examples/plotting/server/abstractrender.py yields....
![ar](https://cloud.githubusercontent.com/assets/2963989/3267190/51361f2e-f2c6-11e3-80b3-66f5833868a5.png)

Currently you have to use `ColorSpec`. You could use just `Color`, but that depends on whether you want a scalar or vectorized values. In the other case you have to use either `DataSpec` or `ColorSpec`. I have a WIP branch where you can just write `Vectorized(Color)`, but that's far from being finished. `transparent` is not implemented. Using any color with appropriate alpha should do the trick.