html treemaps

- generate treemaps by running python render-graphs.py
- browsers with no d3 support will ajax in the html treemaps
add in a title attribute to the treemap nodes
Try to make phantomjs script more robust
Rename treemap fallback scripts
Rename file like python

@gtrogers, @maxfliri
WIP
Retry generating treemap fallback
Remove duplicate file and run from build_artefact
Merge pull request #95 from alphagov/html_treemaps

Html treemaps - merging this because it needs to be tested on the preview CI box.