add geofencing support

[aaronpk]

I'd like to be able to define geofences and rules that will run whenever a fence is entered or exited.

Currently I do this with an external script that receives the "ping" from Compass whenever a new location is received. It would be nice to have it integrated and have a better UI.

• [ ] create and edit geofences
• [ ] define actions on the geofences (enter or exit)
• [ ] support circular and GeoJSON fences
• [ ] run a web hook when the fence is triggered

There should be meta-geofences created by default for locality, region and country boundaries, triggered off of the geocoding done with each location. You should be able to define a web hook to run whenever the locality changes for example.

[aaronpk]

This looks like a nice project to use to implement the feature http://tile38.com/topics/geofencing/