Also understand the concept of missions which cannot be edited

Also much other cleanup/change

- New MissionManager
- Plumb MissionManager through MissionEditor
- Mission Editor supports get/set

- Restructured a number of MissionItem properties as well

Plus lots of other cleanup

Initial rendering of Waypoints

Some more bugfixes and improvements for the Mission Plan widget. The "current"-checkbox in "Onboard"-waypoints can no longer be changed by clicking directly, but it is handled internally by QGC. Now there should be one and only one checked checkbox, which shows the last KNOWN "current" waypoint on MAV. The white border around an unchecked checkbox means, that the user is requesting the change of current waypoint, but QGC has not received MISSION_CURRENT message as a confirmation yet. Also,if there is no response from UAV after pushing "Read" or "Refresh", the "Onboard" list will be deleted to indicate, that there is no information available.

Working WP manager -> map waypoint updates. List reordering does not work yet. Next steps: List reordering, map -> WP manager updates, better waypoint graphs

Refactoring WP interface, somewhat brittle and untested at this point - use the master branch if you need stable code right now

Changed waypoint list file format (old files are not compatible anymore!), added file version check, now all waypoint entries should have an entry in the waypoint list file - although qgc does not use/read the orbit_direction and param1 fields. QGC writes the value of orbit into param1 and 0 to orbit_direction (this should and will be changed later!)