Add option to disable auto-packing

[vrad-exe]

When editing custom textures or models, auto-packing can be somewhat annoying because it requires you to recompile the map every time changes are made. An option should be added under the Development tab to disable auto-packing. When off, only dynamically generated files (like the music soundscript) and files specified in comp_pack entities would be included.

[TeamSpen210]

Good idea!

[vrad-exe]

Actually, maybe just always disable auto-packing when in preview mode? It's not really needed, since you'd have all the resources. It would still be used when publishing of course.