Allow areas to be optionally open to all other users

In other words, you can retain ownership of an area but disable and
re-enable the protection aspect at will, via the area_open chat command.

By default, nothing is any different following this commit - all
existing areas are protected, as are new ones. But you can do (for
example) "area_open 1" and if you're the owner of that area, it's
now possible for other users to interact there. "area_open 1" again to
toggle the protection back on.

Where there are sub-areas, the main owner and ALL sub-area owners at a
particulare location must have set the areas to open to disable
protection.

api.lua

@@ -24,7 +24,9 @@ function areas:canInteract(pos, name)
 		if area.owner == name then
 			return true
 		else
-			owned = true
+			if not area.open then
+				owned = true
+			end
 		end
 	end
 	return not owned