OCP: AV.io mounts

Clamps for Epiphan AV.io video grabber (all variants). This is part of a set of models to build an Opencast capture agents.

The idea is to have one AV.io mounted using one avio-mid, a second one using two avio-side and then a power supply using a model like powersupply (this model is for one from a DELL mini PC).

Both AV.io's, the power supply and the mini PC were meant to be mounted in a 19" rack adapter.

All parts are mounted from the bottom using 4mm metric screws. A nut is put over the holes from the side.