Add an option to categorize your crafts

The addition of different custom headers and the like will make organizing and finding crafts in the builder’s menu just a bit easier. Its design can be similar to how Steam games can be organized in your Library.

Example:
REALISTIC CRAFTS [-]
-Saturn V
-Redstone-Mercury
-Falcon 9
FICTIONAL CRAFTS [-]
-Interstellar Ranger
-Endurance Space Station
PLANES [+]
CARS [+]
WIP CRAFTS [+]