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)

Fixed print here and a use of iteritems in server/views/data.py


On Fri, Jun 13, 2014 at 8:06 AM, Mateusz Paprocki <notifications@github.com>
wrote:

> In bokeh/transforms/ar_downsample.py:
>
> > +
> > +try:
> > +  import abstract_rendering.numeric as numeric
> > +  import abstract_rendering.general as general
> > +  import abstract_rendering.infos as infos
> > +  import abstract_rendering.core as ar
> > +  import abstract_rendering.glyphset as glyphset
> > +except Exception as e:
> > +  print "\n\n-----------------------------------------------------------------------"
> > +  print "Error loading the abstract rendering package.\n"
> > +  print "To use the ar_downsample module, you must install the abstract rendering framework."
> > +  print "This can be cloned from github at https://github.com/JosephCottam/AbstractRendering"
> > +  print "Install from the ./python directory with 'python setup.py install' (may require admin privledges)"
> > +  print "Questions and feedback can be directed to Joseph Cottam (jcottam@indiana.edu)"
> > +  print "-----------------------------------------------------------------------\n\n"
> > +  raise e
>
> Make sure your code is Python 3 compatible. Here use print(...) and from
> __future__ import print_function, but most likely there will be other
> issues, e.g. iteritems().
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/ContinuumIO/bokeh/pull/707/files#r13747455>.
>