Feature: Docker container for uberXMHF on Raspberry Pi 3

To simplify the requirements for building the Raspberry Pi 3 hypervisor, I made a Docker container with the required files and version dependencies. This Docker container has the baseline hypervisor files built, ready to be transferred to an SD card (using the transfer.sh script).

These files are in a PR for feature-docker.

Merged PR into develop. Thanks for automating this @Cap!