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

Now if the CF disconnects, the state goes back to motors off so when we start over we dont have the device flying

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

added buttons to take off and land, some guards in take off and landing, and feedback from flying state to GUI

Reconnection working now. Need to discuss if it is better to have scripts called from GUI or the way it is done now

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