Enable brush transformations

[BHSPitMonkey]

Brush types (Solid, Block, more in the future?) need a way of being transformed beyond simply setting their dimensions and origin positions. Scaling, moving, and especially rotation all need to be possible.

Should these transformations be a kind of Solid method that immediately mutates all of the planes/vertices therein? Or should it be an instance attribute that is only applied when the object is serialized? Should the code live in the Solid class (is this even possible to do?) Or will such functionality need to be relegated to helper classes like Block?

This ticket can serve as a notepad for this kind of discussion/decisionmaking.