3427: load SP maps in MP, devgui crash fix

Visit: https://github.com/xoxor4d/iw3xo-dev/wiki/Changelog for the latest changelog in case I missed something here.

[General]

• make SP maps loadable in MP
• add mod spmod (custom map gsc/createfx and globallogic tweaks)
• updated iw3xo_xcommon
• fix a crash when opening the config tab within the DayAndNight devgui tab

loading SP maps:

• load spmod
• use gametype dm
• devmap coup (or any other sp map)