Display window for choropleth map

[KatiRG]

Values for choropleth map displayed in a window in upper right of the map.
Adapted from http://leafletjs.com/examples/choropleth.html.

Big thanks to @akurniko for getting it to work!

[gordonwoodhull]

Thanks! This will help a lot.

Hmm, it looks like you're following a different directory structure, closer to Boyan's. I should be able to sort it out, but if you feel like adapting your work to fit better, the idea is to generate dc.leaflet.js from the files in src/ using grunt. The demo now lives in web/ and its dependencies in web/js.

In any case, it's not a big deal for me to pull the parts I like and rework them to fit. I'm not the kind of maintainer who just presses the big Merge button. (Unfortunately my turnaround rate can be a bit slow because I'm careful.)

[KatiRG]

OK, I have rearranged the directory structure. There are only two files that relate to this PR: web/index.html which contains the css for the map window, and dc.leaflet.js which I put in both web/js and the main directory. I haven't generated any of the derived files though (dc.leaflet.js.map, dc.leaflet.min.js.map, etc) since I'm not sure how this is done. If you want me to do that, I can try. Please let me know if I should do anything else. Thanks for your help!

[gordonwoodhull]

I reviewed this again because I was wondering why I never merged this. It looks super useful.

If anyone wants to push this forward, the changes should be applied to the individual files inside src/, instead of the generated artifact dc.leaflet.js