Structure handlers to allow .get() to return lists

See #1154. In the end I didn't modify the Attributehandler and
TagHandler like this, instead I added the `return_list` argument
for cases when one wants a guaranteed return.

evennia/commands/default/building.py

@@ -1841,7 +1841,7 @@ class CmdLock(ObjManipCommand):
         obj = caller.search(self.lhs)
         if not obj:
             return
-        caller.msg(obj.locks.all())
+        caller.msg("\n".join(obj.locks.all()))
 
 
 class CmdExamine(ObjManipCommand):