Allow Zoom levels on the World Map.

This request is inspired by the MCP option that show more of the land. The original engine has a limit and can’t zoom out more that is already achieved.

I think it would be cool see Morrowind and Tamriel Rebuit and the future mainland expansions at once in the World Map.

https://wiki.openmw.org/index.php?title=MCP

"Implements two zoom levels for the world map."

(RM-3616 from redmine: created on 2016-11-06 by Amenophis ., )