Raspberry Pi 3 backup server

Building on the popularity of the same design for the Raspberry Pi model 1 [[link](http://www.thingiverse.com/thing:3732135)], I redesigned the mount with screw holes for the Raspberry Pi model 3 (and later).

The design consists of two parts, a "top" plate interfacing the Raspberry Pi and the "bottom" mount that holds the SSD drive. The 2.5 mm nut cases have been adapted so that they are flush with the mounts inner surface.

Ventilation notches are the same as before.

I also use this setup to host a Nextcloud server for a private cloud service [[link](https://git.open-source.se/henrikcarling/install_nextcloud_on_raspberry_pi)]