Mapping cultural traits & environmental variables onto language phylogenies

First version, basic implementation of #112 for culture variables and environmental variables.
Requires ete2 (http://etetoolkit.org/).  I haven't changed any of the settings files (except my own settings.py) but need to add 'ete2' to INSTALLED_APPS.

Rearranged some of the api_views and wrote an api_view that returns all the newick tree strings.
Wrote api_view to bin environmental data.
Created serializers for a NewickResultSet.
Pruning of trees using ete2, although this throws an exception if the Newick string doesn't use isocodes for leaf names. 
There is JavaScript code in tree.js that prunes trees (again, only works for isocodes) that doesn't throw an exception (just doesn't display the tree) - although this isn't used I kept it in for now just in case.

Can download trees as SVG images.