Whitelist map images from OpenStreetMap

OpenStreetMap provides map tiles, which are used by multiple websites. At present, PrivacyBadger makes the maps disappear from those third-party sites. This should fix it I hope. (This is analogous to the case of google maps)
Whitelist maps from further OpenStreetMap sites

Further OpenStreetMap tileservers, as in previous commit
Merge pull request #177 from danstowell/patch-1

Whitelist map images from OpenStreetMap