Move P_SpawnMapThings before P_SpawnSpecialsThatRequireObjects.

Do not remove special from lines with ML_NETONLY or ML_NONET until after
slopes are spawned.

- Fixed last place elimination not working (again)
- Replaces squishing from level geometry with good old fashioned crush death

Slopes in a few maps are really broken ... think it's anchors, I'm gonna leave that to jart :V

Revert a bruh moment from 2.2's development where, in order to fix statues and spikes from being visible on the death pit in CEZ, I made any object that comes into contact with a death pit and isn't on a whitelist delete itself.

(Now the Chao at the start of Sonic Speedway don't die immediately.)

Kart's manual player friction adjustments were being called after movefactor was reset, meaning friction changed but movefactor was default, essentially creating old 2.1 friction again

(Also removed a bunch of instances of PF_SPINNING since we haven't used it)

Vertex snapping 'slope anchors'

See merge request KartKrew/Kart!317

By pretty much restoring the old musicdef system, I tried to work with it but couldn't, if needed that can easily be brought back later on.

This makes FOF sloping over other slopes possible!

Had to remove the absolute height function though.

Requires spawning fake floors before slopes, and therefore before things,
basically before everything. Hopefully nothing breaks!

Previously it just used the first three anchors that had snapped to a vertex
in the sector.

btw fuck DOOM

There are some issues I ran into:

- Rotation is jittery (not introduced by this commit)
- 2P is wack, I don't care

Object tracking is off, but it was off before so I don't know if I actually
broke it. Minor refactoring in HWR_RenderPlayerView and HWR_RenderSkyboxView.

* Introduce SPR2_XTRA for face graphics, since the current system is prone to plenty of conflicts with modders if you're not careful.
* Fixed a bug where you'd see :nick: on the current character selection screen if you didn't have many skins loaded.
* Fixed a bug where character skins loaded in PK3s would attempt to load every single lump of the PK3, even if it wasn't in the same subfolder as the original S_SKIN, as a sprite into the player struct. Could stand to be ported to vanilla.

Requires new chars.kart, which was created using the help of the indev 2.2-based Kartmaker update which will be available shortly.

Fixes a duplicated condition which sends the player back to the title screen under advancemap next. Teeechnically does stuff for issue #91, but I'd like to take a more thorough approach later once I've got consent for a potentially radical change to this currently useless feature.

Fixed a crash I recieved while playtesting bots on Petref which was caused by an invalid subsector reference. This can only happen when the mobj was removed. I have no idea how or why this wasn't caught earlier, but I suspect we inherited this issue from upstream in the merger.

KARTKREW is 640x400 LOL

Fix the issue where skincolor and character (and inadvertedly, name changes and followers) would not be sent to the server, leading to the 0,0 Ashura bug.

Fix the weird "Eggman is not a colour" print by fixing the code that overwrote your skin and colour willy-nilly, and then disabling it (it was a mistaken element of the port).

Temporarily disable the POSITIONI sweeping for the first 16 tics of map drawer. (Looks better for if we showcase 2.2 merge footage before creating a better title card).

* Fix the title card fade's one-frame invalid memory read.
* Disable a redundant gamestate-activated wipe, which A) horribly broke Encore wipes, B) made normal map transitions take longer than they should, and C) held on the one glitchy title card wipe frame to make the game look more broken than it was.
* Fix Encore wipes being broken by the merge.
* Disable (not remove; may want to use later) the :nick: patch draw attempts from the title card drawer.
* Re-add zonettl support to the title card drawer.
* Move the title card drawer in front of the fade (Looks better for if we showcase 2.2 merge footage before creating a better title card).

Add a mechanism where in DEVELOP builds, you can use any feature that doesn't have an unlockable in the listings attached to it.

This is necessary to test fixing wipes, because Encore mode is currently completely inaccessible otherwise.