Mgv7: Remove mountain height limits, don't let mountains chop dungeons. All mapgen: generate dungeons throughout world

![screenshot_2645831388](https://cloud.githubusercontent.com/assets/3686677/5584415/2aa2fc18-9084-11e4-9b58-96f3831e9d90.png)

Currently mgv7 mountain height is range limited between 80 and 150, remove those limits to enable modification through .conf.
Currently dungeons are only generated in and below surface mapchunks (the mapchunk containing sea level). Enable dungeons throughout world in mountains and floatlands.