Offer Openstreetmap map type in google build flavor

[jidanni]

Here we see several choices, but they're all actually just the proprietary Google map.

Soon there's be some other choices, like Openstreetmap?

[goldfndr]

#394

[barbeau]

Thanks for the report! Yes, a discussion surrounding this is in #394. Basically, there is a separate OSS version that includes OSM maps. I'll keep this ticket open for adding OSM tiles as a map type to the google build flavor in case someone wants to take this on.