New module: msgscancfg.js to replace copy/pasta msg config menu in *.src

Also added 2 new menu options:
R - re-load msg scan config & pointers
W - save msg scan config & pointers

Leaving the menu file named "maincfg.msg" even though that's a pretty
badly named file - should rename that file at some point, but keep 8.3
format for DOS (e.g. TheDraw, AcidDraw) compatibility.
mscancfg.msg maybe? Ah, the fun of abbreviating things to 8 chars again.