5 degree symmetry snapping in addition to stock 15 degree

[Burninate]

72 positions in a 360 degree rotation gives you 3*3*2*2*2 divisions. The parts are configured to allow 72-way rotation (5 degree gradations if you hold shift) right now. What's missing is placement. Move a part with angle snapping around a large object, and it jumps in 15 degree increments. Without angle snapping on at some level, it's impossible to precisely place matching parts. Keep 15 degrees as the default, but allow us a button to change it to 5 or 10 (or 30 or 45) as well.