Trigger camera at start of mission.

[javatechs]

Camera must be reset at the start of each run.
@pryme , please test
Camera is reset each time exec receives
rostopic pub /exec_command robo_magellan/to_exec "{cmd: 'START_EXEC'}" -1s

See commit
beaed89

[pryme]

@javatechs This does not seem to work as is. When run as described above, the touch switch is not detected. However, if rosservice call /mavros/cmd/command 1 203 0 0 0 0 0 1 0 0 is called, then the touch switch is detected.