Feature/windshaft indicators 2

Kind of a big one, touches all parts of the app.

Basic idea:
  - Add the_geom column to transit_indicators.Indicator
  - In scala, cache the geometry associated with that indicator when the indicator is calculated
  - geometry as_text POSTed to the Django API along with all other indicator data
  - Windshaft draws directly from the indicator table, using the params given in the URL

In most cases, the_geom will be the same for all indicators of a given aggregation type, same with Windshaft styling (e.g. ntiles for route aggregation, and most likely mode aggregation)

Quite a few TODO's scattered throughout the code, but are mostly relevant to other future tasks and are left as notes.
Just submitted a PR to Leaflet.utfgrid that adds a redraw function to match TileLayer

https://github.com/danzel/Leaflet.utfgrid/pull/27