removed the cpp GUI application (was not such a great idea, after all)
arduino - Display - fixed init() method to allow re-initialisation
	- sending the init command 3x to make sure the display gets reinitialised in both 8-bit and 4-bit modes
arduino - main - implemented simple commands based on the buttons pressed; printing out received gcode
command_line - implemented simple command response and gcode sending
	- removed interface (not needed anymore)
	- document - added missing methods
command_line - CMakeLists - cleaned up and added -Wall -Werror