2019.4.1.21 - some QoL stuff, plus fixes

Added some stuff:

• Fixed heightmaps (the images should work with other programs now)
• Refactored lots of editor modes - no features should have been changed but hopefully it'll make the code easier to work with
• Refactored a bunch of things in addition to that
• Added tooltips as a super basic documentation feature (these can be turned off in Preferences if you find them to be annoying)

I also took the version numbers out of the filenames, to make updating somewhat easier. The old ones are hidden on Itch, but if you want them they're still in the Github releases.