Add filters folder to organize filter designs

[scottyallen]

What do you think about moving Gas_Mask_Male_Thread out into a separate set of f3z/step/stl files in the parent NATO_40mm folder? That seems separate to your specific canister design, and useful for others to see/reuse.

[stephen304]

@scottyallen I actually have no idea how that works - in the f360 cloud the thread files are in my folder and other people have imported it. Maybe we can have a util folder or something, but someone else would have to do that since I don't use fusion