travis: drop older distros

ev3dev-stretch: add pybricks-micropython package

ev3dev-stretch: add pybricks-micropython package

ev3dev-stretch: add pybricks-micropython package

ev3dev-buster: nice limits for robot user

This adds a config file to allow the robot user to set niceness to
max value, e.g. using the nice or renice command.

ev3dev-buster: set nice and use PAM in console runner service

Setting nice makes user programs run with higher priority, which is
helpful when you have a tight control loop. Also having a proper PAM
session fixes some permission problems for things that use PAM for
authentication. It also has the side effect of setting the owner of
the tty so we no longer have to do that explicitly.

ev3dev-buster: add more rpi device tree blobs

also fixes build failure due to renamed rpi zero device tree file

ev3dev-stretch: can't install python3-agt for rasbian

ev3dev-stretch: can't install python3-agt for rasbian

ev3dev-stretch: drop libgrx-3.0-2-plugin-linuxfb

This should be included automatically by libev3devkit now.\

Issue: ev3dev/ev3dev#1275