Beamer adapter arm - for Optoma (and others)

### Why

I was printing the excellent beamer-to-tripod adapter made by Klenzel: https://www.thingiverse.com/thing:2638768

However, the arms were too short to reach the M4 screwholes on my Optoma beamer. This bracket is designed to interface with his part, but increases the bracket length from 70mm to 94mm.

### Features

* Interfaces with Klenzel's tripod beamer mount
* Tested with an Optoma beamer, should work with most beamers that have their mounting holes spaced a bit more distant.