GoPro simplified clip mount

I've found that other GoPro clip mounts are fairly slavish reproductions of the originals. Which would make sense if we were doing injection molding, but they're always far more finicky than they should be.

This is a replacement mount simplified and tuned for 3D printing. The tolerances are such that it might only work on my own printer, but there's (bad, very bad) OpenSCAD source if it doesn't.