- Restructured a number of MissionItem properties as well

Plus lots of other cleanup

Initial rendering of Waypoints

Do not dynamic cast or de-reference QObject, since object is either in
destructor or may have already been destroyed.

This is the Pixhawk research board, not the PX4 production board.

Disable the active WP setting in the edit list, as its super error prone - only allow it in the view list and switch between views based on activity on the system / UI

The background color of the mission items is now controlled by stylesheets as well. This change also fixed restyling the mission lists when a style change occurred.

The View Only waypoint view is now styled similarly to the editable view. Same caveats apply where the widgets don't update their style if QGC has its styles changed.

The editable waypoint view has been completely reworked from a styling perspective. Now both the light and dark styles work great, though switching between the styles doesn't work as expected yet. That's still to come.

qgcunittest.pro now compiles and runs as long as run in terminal in projcts->Run Settings is unchecked.

Mission Plan Widget: Added support for MAV_CMD_DO_SEARCH custom pixhawk commands, fixed some tooltip bugs.

Remake of "editable" mission elements is now complete and usable. Missing widgets for Takeoff and Land will be added soon.

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.

Finally resolved waypoint positioning issues, 2D and 3D map work now nicely together with less flicker