Updates and fixes for the ZB config

See merge request STJr/SRB2!859

Skip empty gametypes in level select menu

See merge request STJr/SRB2!819

Remove the multi-file ZB configs. We're stick with the single-file config for ZB and doing all the UDMF stuff in UDB

NiGHTS Mode menu fixes

See merge request STJr/SRB2!841

Fix division-by-0 crash from 100% gamepad deadzones, and lack of input from 0% deadzones

See merge request STJr/SRB2!838

Actually use the "SCREENSHOT OPTIONS" header for its menu.

See merge request STJr/SRB2!832

Skins refactor

See merge request !843

Fix NiGHTS Attack crash after render mode change

See merge request STJr/SRB2!837

Fix HWR_DrawFlippedColumnInCache ignoring chroma key TF

See merge request STJr/SRB2!826

Replace NextTexAvail with glGenTextures

See merge request STJr/SRB2!828

Fix ASTBlendPixel blending with nothing

See merge request STJr/SRB2!827

Archive sprite2 Hotfix

See merge request STJr/SRB2!845

Fix desyncs never recovering if node and player mismatch

See merge request STJr/SRB2!842

One line fix: don't assume 0 (aka SPR2_STND) is the default value for sprite2, but rather what the state sets for it

This fixes some issues with a custom character tested during netplay, which did not have SPR2_WAIT sprites and therefore fell back to SPR2_STND sprites. Unfortunately, the fact they used SPR2_STND instead meant the sprite2 was not synced at all!

(oddly enough, this actually revealed some secret file dependencies previously included via r_things.h! I also needed to include d_player.h in r_skins.h itself it seems)

Set the "spritename" variable within R_AddSingleSpriteDef rather than externally to it, since R_InstallSpriteLump is the only place it gets used anyway

This way we don't have to make it some extern in order for r_skins.c to use it

It makes more sense for 100% deadzone to just make it so that
you have to push the axis all the way to trigger it,
rather than 100% deadzone resulting in no axis input
ever happening... So, let's make it be the former way instead

Fix division-by-0 crash with gamepad deadzones
The problem was that it checked if A was more than B,
then lowered A to a max value, then subtracted B from A,
then divided something by that, without checking if A minus B was 0,
allowing division by 0 if B was the same as that max value

This fixes that by making sure that A is less than the max value

Fix -OGLlib

See merge request STJr/SRB2!794