fix permissions for some edit commands

- always allow read-only edittextureslot, editmapmodelslot and
  editmapsoundslot
- allow setvantagepoint when editing offline or spectating offline
- new var editing_sp: 1 during edit mode in singleplayer (offline)
- additional menus for read-only access to map config slots
- new bonus edit scripts: selectmiddle and unclipentclippedmodels

DOCREF edittextureslot editmapmodelslot editmapsoundslot setvantagepoint
DOCREF editing_sp

source/src/worldio.cpp

@@ -485,7 +485,7 @@ COMMANDF(clearvantagepoint, "", () { if(!noteditmode("clearvantagepoint") && !mu
 
 void setvantagepoint()
 {
-    EDITMP("setvantagepoint");
+    if(multiplayer("setvantagepoint") || (!player1->isspectating() && noteditmode("setvantagepoint"))) return;
     clearvantagepoint();
     short p[5];
     storeposition(p);