Fix build management / CI

[barulicm]

All of our branches are failing CI because the repo lacks a real build system.

My idea is to add a top-level makefile that can be used to build and upload any of our firmware targets. It could, for example, use the Arduino CLI.

Once this build system is in place, our CicleCI can be reconfigured to build all of our firmware targets and return to usefulness.

This will be a post-IARRC 2018 task.