Added CurrentPosition model, geolocation api

Router uses geolocation api to update the CurrentPosition model
singleton.
Changed to watchPosition, only for main view

Switched to watchPosition to get better accuracy and I might want to
plot the user's current location as well.  Also, only doing this for the
main view (although for now there is only one view).

One TODO here is to stop watching after some period of time, to conserve
battery, but I'll need to test to see what kind of delay values make
sense.
Don't need Position class, so removed
Split out a RouteEditor, included in MainView