Initial

- Created framework
- Added ability to set: length, background, music, add entity spawns,
add boss spawns, pattern spawns and manipulate the map tree.

TODO:
- Implement dialogue (both into Project Utopia itself, and the level
editor)
- Save your progress, i.e. export the tree without compiling it.
- Add help references, i.e. tell the user what each option does.
- Change object ids (i.e. pattern ids, entity ids and boss ids) to make
them easier to input. Limit them to the CORRECT entities, unless I
implement custom entity and pattern loading.
- Lock the save dialog to ONLY allow saving of .upa files.
- Make nodes more obvious. i.e. allow the user to name the nodes
themselves, so they know what each node means instead of BOSS_1 or
PATTERN_1