Leaflet source

[stuartpb]

Right now I'm still pulling Leaflet 0.5 from MapBox's CDN. I should pull it from somewhere else, and a later version (I think they're close to 0.8).

[stuartpb]

Leaflet's 1.0 release (the one that was going to be 0.8) is still a far way off: https://github.com/Leaflet/Leaflet/milestones/1.0-beta1

Nonetheless, we might as well move to a self-hosted 0.7 until 1.0 hits.

[stuartpb]

Requires compatibility check for marker clustering and view restoring plugins.