Fix wrong minimap scales on Dance, Implosion, Space-Elevator and Xoylent

Thanks @SirRanjid for sharing this tip on Discord after running into the same issue on his own map :D

If the size of the lightgrid area is not set in the mapinfo, the minimap won't be scaled properly.
Dance, Implosion and Space-Elevator are 3 official maps that use lightgrid brushes and their minimaps are indeed at the wrong scale.

Xoylent doesn't have a lightgrid brush but its minimap is also at a largely wrong scale, maybe because of the _skybox entity. Setting the map boundaries in the mapinfo seems to do the trick.