Feature Request: Brush creation

[snake-biscuits]

Add a function / method that adds brushes from a box selection (vec3 min & max)

Procedural shapes:

• Pre-clipped stairs with pretty random texture offsets
• Arch
• Cylinder
• Spike

All with similar parameters to what the Hammer Editor offers

[snake-biscuits]

Since this will be used by QtPyHammer for a lot of editing operations, all actions will need to function as a CRDT
Everything must work with PyCRDT
This means undo & redo for everything, though actions such as a series of similar actions (nudging into position) will be merged into one