Google Maps Plugin

Provides embed `iframe` and `thumbnail` via static maps. I could provide more `thumbnails` with different resolutions. An API key is optional for the `thumbnail`, but if you make more than 25.000 static map requests a day (download of thumbnails) you need a business account.

I used the rel type `reader`. Maybe there should be a new one `map`? I think I'll also add OpenStreetMap support (not today).