Changes to comments in PPS Client (attempt to make style consistent with controllers), and added Emergency stop button to GUI

The coordinator row and (dis-)connect,  start-stop bar are now fully connected and fully generalised for operating as both an agent and a coordinator GUI

Added things to GUI: red rectangles to indicated an occluded measurement, and unavailable image for battery and flying state

Added files for the flying agent GUI, currently compiles in Qt but need significantly testing and development for integrating with ROS