Mission module for rotorcrafts

1) Mission module sources for rotorcraft and fixedwing splitted
2) Mission navigation handler(mission_rotorcraft_nav.c) for rotorcraft added
3) 'duration' for wp/segment/path is interpreted as the stay time in proximity circle, duration <=0 neglected
4) 'duration' for circle is interpreted as duration while drawing circle ,  duration <=0 neglected
5) handling of mission commands from datalink for nps added, this feature can be enabled by 
    <configure name="USE_MISSION_COMMANDS_IN_NPS" value="1"/>