Brushes

[alikindsys]

Add the ability to make custom brushes so selections aren't limited to being just cubes.
The brushes will be "rasterized" into the octree volumes once they are added to a zone so that brush data is ephemeral and all changes to zones are immutable, being revertible at any moment.

This implies that a zone must keep the history of changes starting from its creation, this is a cool thing to add as well so I might add that too.

An example of such a brush would be the cylindrical/triangle/n-gon brush.

[alikindsys]

Fix: Brushes are what will be permanently stored. Octrees are an in-memory data structure.