HUD fixes

See merge request STJr/SRB2Internal!234

Rain fixes and associated

See merge request STJr/SRB2Internal!233

Drawangle fixes

Closes #153

See merge request STJr/SRB2Internal!236

Prevent just anyone from skipping credits but allow admins

See merge request STJr/SRB2!478

Pk3 Leaks

See merge request !500

* Re-fix chat HUD position, and make it not move in match (which it needed to do in 2.1).
* Fix HU_drawPing for the new palette.
* Change the condition for greying out players, since the current one was buggy.
* Allow for tokens on the coop MP HUD, and use the small emeralds so there's space for them.
* Fix the mapping between skincolours and name colours in new chat, specifically to take into account every possible text colour (as opposed to the port previously done, which only used the 2.1 text colours and looked like ass as a result).

* Move HUD text's anchoring to underneath STR instead of above Lives.
* Adjust chat position slightly, to take advantage of SRB2's HUD layout having less content towards the bottom (unlike Kart, where it has roughly equal).
* Fix Match emeralds not displaying while in tab rankings with all-seven invuln/shoes bonus active.

* Like Kart, remove cv_precipdensity.
* Like Kart, replace "Infinite" draw distance value with "None".
* Better thinker with more return optimisation.
* Better placement of thinking in rendering, to avoid ceiling-mounted sprite glitches.

ACZ hardcoding (including minecarts)

See merge request STJr/SRB2Internal!231

Stand(alone) lump comedy

See merge request !499

FOF slopes level load fix

See merge request STJr/SRB2!498

libopenmpt support

See merge request STJr/SRB2Internal!229

Fix warnings/errors found during compiling, mostly of the mixed-declaration-and-code or shadowed variables variety

Part 2 of fix, make sure copied slopes also pass on hasslope status to attached target sectors for FOFs

Also fix whitespace to use tab-style spaces instead of regular spaces, ew

Fix FOF slopes briefly glitching on level load in software mode, by ensuring the FOFs' target sectors have hasslope set on creation