[MP4][AllEnv] Editor: Alphabetical sorting of signs

[rachovolker]

Currently, Signs/Ads in the Editor get sorted alphabetically ignoring the folders they've been placed in. Since mapping for different competitions requires different Sign-packs, these signs can be quite hard to find among the 30-50 pages of signs. My current solution of removing every signpack I don't need for mapping at the moment can get quite annoying when working on multiple maps using different sign-packs at once.

I'd also love to see a query before opening maps in the editor asking which Sign-pack/Folder I want to use for this track. Maybe make it available by pressing Ctrl, like we use to change Mods/Moods.