Add orientation support

Orientation is specified in radians, range is [-2 PI, 2PI]

in order to call from CLI use

rosservice call /ardrone/setgpstarget "target:
  id:
    uuid: "123456789ABCDEF"
  position:
    latitude: latitude
    longitude: longitude
    altitude: altitude
  props:
  - key: 'orientation'
    value: '6.28'"