Refactor airframe configuration module to use enum values instead of combobox strings

I also refactored UAVObject data calls so that it calls with the preferred method, instead of trying to look up the field at runtime.

This is tested and works, but there's a known bug by which save has to be clicked twice when changing vehicle category (multi/heli/custom), etc.., but not vehicle class (quad/hexa/octo, etc...). Watching the UAVO browser, it is clear that the SystemSettings object is updated on the flight controller, but for some reason it is only committed to RAM, not saved. It is a mystery to me why this is, and if someone has an idea about where this is coming from I would appreciate the tip.