Draft: Implemented loading bundled campaigns

[GaidamakUA]

TODO: Probably, it's better to create bundled dictionary automatically @czlowiekimadlo What do you think?

[czlowiekimadlo]

Indeed, you could create bundled dictionary automatically using the Directory class, though that would require some more tinkering, as special-purpose maps would need to be separated, and additional metadata, like "online_id" would need to be moved into the map file itself.

[GaidamakUA]

@czlowiekimadlo Fixed issues, you've mentioned. Please, squash commits while merging and give it a good name. And sorry, screwed up history of map_loader.gd should've used merge and not rebase. You might want to reread map_manager.gd. Since we now have bundled field, I decided to add bundled maps directly to maps dictionary.

[czlowiekimadlo]

Thank you very much for your contribution!