Allow rotation and mirroring of gadgets like traps

[Forestidia86]

Currently traps can't be (visually) mirrored or rotated. Hatches can be mirrored for different orientation.
There can be a usecase for such operations on traps, especially if they are not symmetrical. Furthermore it can probably avoid special cases for these objects.

As a sidenote there is an issue (#273) that mirroring of gadgets can lead to them moving if they have certain meassures.

[Forestidia86]

After thinking about it a while, I see that it could lead to problems animations- as well as physicswise.
One problem talked about were the flinging gadgets which should behave according to their orientation but that would need defintions for all orientations.

I still plead for having mirrored versions of the asymetric traps like the porcupine.

[Simon]

Right, this is a complex topic. It touches level format issues and thus backwards compatibility. I'll have to elaborate here, these days.

-- Simon