2.0 bugfixes before new content

EDIT TWO DAYS LATER:

• corrected a minor error in the library mod that likely wouldn't have popped up in the context of 700,000 mutations
• allowed mutbutton scrolling code to work when multiple mods are running it at the same time (copying and pasting)

EDIT END

Some of these bug fixes are major.  Updating is highly recommended.

• fixed weirdness with mutation selection and modded mutations

This includes, but is not limited to, duplicate mutation buttons and a bunch of extra choices that shouldn't be there.

• added manual prismatic iris compatibility for newer Defpack versions

Loading Defpack 4.2 and 700,000 mutations would cause a fatal memory error if prismatic iris was rolled to be chosen.  Technically an issue on Defpack's side, hopefully it'll be fixed later.

• re-added heavy heart being guaranteed in the first choice after three weapon mutations
• updated logic to determine when mutations should be replaced with merged ones
• extralevels shouldn't draw HUD elements over the credits anymore
• fixed merged crowns occasionally not being selectable (I hope)
• fixed "can't call instance-specific function" errors with merged crowns

..and a few other minor things.

As always, if you find some sort of bug or error, please do not hesitate to let me know so I can fix it.