[Feature] Rotating Levels Ingame

[albertz]

Converted from SourceForge issue 2826886, submitted by nobody

After playing around with the Level Decompiler, an idea came about of a possible addition to levels. While making a level, one could put a target, just for example, that flipped the level around 90 degrees. It would increase level playability and possibly add more fun to the game.

[albertz]

This should be a client side option which specifies the rotation. Not sure if we should only allow multiples of 90° or any.

Also other operations like mirroring, stretching, etc. may be possible.