Backwards incompatibility: rangefinder needs exporting for simulation in custom sessions

[klaxalk]

If you have a custom tmux/tmuxinator session, please add the following export to the pre_window line:

export SENSORS="garmin_down"

similarly to as it is in here: https://github.com/ctu-mrs/simulation/blob/master/example_tmux_scripts/one_drone_gps/session.yml.

This is now needed to inform the mrs_uav_odometry node, that the downwards-pointing Garmin range finder is present. Without it, it will not wait for its data and it will not fuse it.