Dual Mount for GoPro

This is a updated version (ported into Fusion 360) of fbuenonet's dual GoPro mount.

Things changed:
- Slightly wider to accommodate waterproof cases
- Full 360 deg rotating arms (requires M5 nut)
-- There are two arms included (mirrored versions of each other), but in reality, only one is needed if you don't care about the nuts being on the same side while the lockdowns are facing away.
- Alternative 90 deg rotated base (both STLs are included)
- Ported to Fusion 360 (file included)

EDIT: I've now updated the photos with the rotated main mount. ~~The photos are of my first iteration which changed the internal supports and didn't include the middle fill area. After some use, I can see that this will be the failure point so I'll eventually reprint it with the current design (which changed them back to close to the original design).~~ On the normal version, it's a very tight fit using a shortened lockdown knob (see the photos above), you might want to print a minimum length ve