[Editor] Some custom tileset suggestions

[Dinosaurismus]

• [ ] Type to select items for custom tilesets (like question blocks)
• [ ] Add ability to store all tileset files in a folder (to reduce clutter)
• [x] Make tilesets able to be exlusive for more than one level

[Wohlstand]

For third: Even SMBX allows to have levels in sub-folders, so, you can put multiple levels into sub-folder and saved tilesets will be shared with them (but check to save episode-specific tileset)