3DHubs integration

[ericrosenbaum]

When I was in Amsterdam I met the super cool folks at 3Dhubs, which is a service that connects you to somebody nearby with a 3D printer. They have a nice API which is apparently easy to integrate:

https://www.3dhubs.com/teleport

We can add a file menu item for it. I think this should be a separate category (i.e. with a horizontal divider), below the export options, that says "Print with 3DHubs..."