added OSM base tile sets, #41

The following sets are included:
* OSM standard
* OSM black and white
* OSM Stamen.com watecolor
* OSM Stamen.com toner
Revert "auto expand graph on startup"

Reverts commits:
f47592c321b681bc0ba41935bd8f1c10b103a573
28c9476a1f4ab82683706a3eff05f23d150ebcac