merged engine menus, native menus, game menus, plugin menus into a single layered menu interface, simplifying all the special-case input.
engine confirmation prompts can now show regardless of underlaying menus, including above the console.
skeletal formats can now provide their own way to build bones, for variable per-bone keyframes/interpolation methods/etc (used by gltf2).
updated various plugins for the new api.
removed qvm makefiles/scripts.
git-svn-id: https://svn.code.sf.net/p/fteqw/code/trunk@5530 fc73d0e0-1445-4013-8a0c-d673dee63da5
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