Move crime heatmap grid into a LeafletJS plugin

- Move all heatmap grid code into crimedb-leaflet.js with dependencies
  on jQuery and LeafletJS.
- The crimedb-leaflet.js code is AMD of course. This should be available
  as a non-AMD file in the future for third-parties to use more easily.
- Change main.js and bin/render to include the reigon name for fetching
  data. This is needed because we don't want to rely on relative paths
  in crimedb-leaflet.js so that it can be used on third-party sites.
crimedb-leaflet.js: Refer to leaflet as L and jquery as $

- Load LeafletJS as the 'L' symbol using AMD so that the code can more
  easily be shared; likewise jQuery with '$'
Move Stamen LeafletJS plugin to its own JS file.

- Create a new AMD module for the StamenTileLayer and use it in viz.js
  rather than implementing inline
Stop loading jQuery UI

- We weren't using it anyway; remove from www/js/ entirely