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.

Started parameter interface refactoring to adhere to MVC design pattern. Working on getting custom widgets completely up and running

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