Unhardcoded teleporter entity

[AllyTally]

Changes:

In an effort to reduce the split between custom levels and the main game, I've made a system where when exiting a teleporter, the player follows a three point Bézier curve. Point A (the starting point) is the teleporter's center, and point B and C are saved in the teleporter's data, along with facing direction, gravity state and the amount of frames that following the curve should take.

Along with adding a teleporter edentity to house this addition, this PR also runs setteleporter() dynamically when loading edentities, much like trinkets.

However, this PR does NOT replace the current system, and is instead locked to editor-only at the moment, for the following reasons:

• The main game does not use the edentity system (this is possible to change, but...)
• There's certain glitches that speedrunners/TASes use, and I don't know much about glitchrunner mode, so I think someone else should do that part.

The PR also contains an editor tool to place them down, which lets you control the points of the curve, and facing direction/gravity state.

Legal Stuff:

By submitting this pull request, I confirm that...

• My changes may be used in a future commercial release of VVVVVV
• I will be credited in a CONTRIBUTORS file and the "GitHub Friends"
  section of the credits for all of said releases, but will NOT be compensated
  for these changes

[AllyTally]

I've pushed a new commit which adds p5 and p6 to the createentity scripting command, since they were added to the internal function.

[InfoTeddy]

Style pass.

[InfoTeddy]

Another style pass.