Plus lots of other cleanup

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.

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.

Cleaned up and commented major code parts. Refactoring HDD and HSI widgets to support QGraphicsView drag-and-drop, tested multi-MAV support more intensely, currently adding the system coloring to all widgets

Major refactoring of the waypoint code. The new design fits the model-view-controller pattern better.

UASWaypointManager now implements the protocol described in http://qgroundcontrol.org/waypoint_protocol