Automate mesh network set up

[ezio-melotti]

Currently, to set up the mesh network there are several steps that needs to be done manually. They are documented here:

• https://github.com/overthesun/simoc-sam/wiki/RPi-Zero-mesh-network-setup

This should be automate in a setup-mesh command on simoc-sam.py.

[ezio-melotti]

See also the following issue, that suggests using NetworkManager instead of BATMAN for the mesh network:

• Reimplement the mesh setup using NetworkManager #107

If we can use NM for the mesh, the automation will be much simpler.