Add a map for boundary-finding and Portland, ME to cities.txt

* The largest body of this PR contains a full-screen map to make it easy to draw the boundaries of a metro area, and presents them in order for insertion into cities.txt. It uses leaflet, leaflet-draw, and mapquest tiles.

* The smaller bit is adding Portland, ME, capital of the lovely state of Maine, to cities.txt

*  I also removed trailing whitespace from cities.txt. I resisted the tempation to clean it up any further.