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)

You use `DataSpec` in Python so you get arrays. You can view `DataSpec` as `Array(Float)`, which can also be assigned a constant scalar value of type `Float` (to save bandwidth, but internally it will be represented as an array of "appropriate" size, which is magic). If you don't want vectorization, then use (I presume) `Color` in Python.