Gametype strings backport

See merge request !473

Allow connecting to localhost / 127.0.0.1

See merge request !474

Because IPv6 doesn't seem to work anyway.

-noxinput and -nohidapi command line parameters.

See merge request !468

Error if the lump is a PNG lump

See merge request !466

This reverts commit d03c5393.

Added the Gametype_Names array and G_GetGametypeByName for ease in converting gametype nums to strings and vice versa

gametype_cons_t is now initialised using the Gametype_Names array, like how Color_cons_t is initialised using Color_Names

# Conflicts:
#	src/doomstat.h
#	src/m_menu.c

Fade out level music during intermission via level header

See merge request STJr/SRB2!470

Custom intermission music by level header [by SteelTitanium]

See merge request STJr/SRB2!469

This reverts commit 8780800e.

CircleCI: test build SRB2 without network support

See merge request !462