new commands to add modeinfo and artist info to maps

mapartist print|set|get|clear

  print:  prints the map artist player ID
  set:  sets the map artist player ID to the currently logged in player
  get:   returns the current map artist player ID
  clear:  erases an existing map artist record in the current map

modeinfo list|get|clear|<modelist> <modeflags>

  list:  lists current modeinfo entries
  get:  returns list of current modeinfo entries
  clear:  erases current list of modeinfo entries
  <modelist> <modeflags>:  specifies flags for a list of modes

DOCREF modeinfo mapartist

source/src/entities.cpp

@@ -623,6 +623,7 @@ void entstats_(void)
     }
     if(es.entcnt[CTF_FLAG]) conoutf(" flag distance: %d", es.flagentdistance);
     conoutf(" map capabilities: has ffa spawns %d, has team spawns %d, has flags %d", es.hasffaspawns ? 1 : 0, es.hasteamspawns ? 1 : 0, es.hasflags ? 1 : 0);
+    if(es.modes_possible & GMMASK__MPNOCOOP) conoutf(" possible multiplayer modes: %s", gmode_enum(es.modes_possible & GMMASK__MPNOCOOP, txt));
     conoutf("total entities: %d", ents.length());
     intret(xmodels + xsounds);
 }