Merge branch 'student_GUI' of https://gitlab.ethz.ch/D-FaLL/PandS-System/D-FaLL-System into student_GUI

custom controller a bit more ready, still need to fill information in GUI fields and connect everything to GUI (set setpoint mainly). Landing and take off parameters now in YAML file

added a different link to set the setpoint for GUI, so that PPSClient decides in the end which setpoint to use. Difference between high-level setpoint and low-level setpoint

Added link to use custom controller and safe controller. Need to see what happens if we change yaml file name on the run

added disconnect command, need to test. Also added protection when disconnected to change flying state. Also buttons are now really disabled when disconnected