Qt5 Path Planner: Need event filter on combox box

Otherwise attempting to select an item in the QComboxBox
makes it simply disappear.  This filters those events from
the background view.

Solution found http://stackoverflow.com/questions/14248036/qcombobox-doesnt-show-its-item-list
Qt5 Browser: Add event filter for QComboBox so they appear properly

Similarly to what was required for the path planner view.