Streamline installation

@hammertoe this branch combines group-nodes-by-itertools and plot-benchmark-results with
streamling of the installation so that plone.app.contenttypes is not required for installation.

Changes:
  - Removed dev.cfg (unifiied setup in buildout.cfg)
  - Moved bechmarks into buildout root (/benchmarks)
  - Split buildout parts into content type specific parts and executables
  - Only import p.a.contenttypes in experimental.securityindexing.tests sub-package such
  - Used itertools.groupby to group nodes in shadowtree
  - Changed benchmark output to JSON
  - Added ipython/matplotlib script to plot results (benchmarks/resultsviewer.py)
  - Added ipython notebook example of benchmark plots
  - Add README.rst in benchmarks
  - Updated README.rst