need FlyTo to ask for the height frame

The FlyTo dialog box on the map currently assumes GLOBAL_RELATIVE_ALT:
https://github.com/diydrones/MissionPlanner/blob/master/ExtLibs/ArduPilot/Mavlink/MAVLinkInterface.cs#L4344
we need the dialog to ask the user what frame they want to use "Terrain Relative", "Home Relative" or "Absolute" and pass that to the setPositionTargetGlobalInt() message.
I just don't know how to create a dialog like that with a float input and a selection drop down with the 3 choices, I will need some help from a C# developer
Anyone flying BVLOS really needs this change