v0.2.1.0

Wow a week without updates? smh smh, what are you all not paying me for.
Fixed some pretty nasty undo-related bugs, some of which could be used to break levels' logic! Undo bugs are hard to find though, so please let me know if you find any. There's a couple other changes, so check out this changelog:

- Added a semi-transparent preview of what a door or key will look like when placed.
- Added the I-view sign on top of the player.

- I-view can no longer be activated in the editor.
- The right dock can no longer be dragged while playing.
- Optimized a bunch of stuff! which might've also caused bugs? Hope not.
- Lock arrangements are now centered (won't stay on the top left corner if you make bigger locks)

- Fixed running off a cliff and picking up a key (or other events) making the related undo spawn you in mid-air (tfw literally an edge case)
- Related to the above, fixed a bug where if you immediately fell after undoing, did something, then undid again, the entire undo may not be registered. What.
- Fixed undoing at the same time that you picked up a key making it be picked up *after* undoing.
- Fixed some inexplicable crashes by updating to a newer version of the game engine. It's an experimental version, though, so hopefully that doesn't cause trouble!