Settings: Proper priority hierarchy

Remove old defaults system
Introduce priority-based fallback list
Use new functions for map_meta special functions
Change groups to use end tags

Unittest changes:
 * Adapt unittest to the new code
 * Compare Settings objects

src/script/lua_api/l_settings.cpp

@@ -197,7 +197,7 @@ int LuaSettings::l_set_np_group(lua_State *L)
 
 	SET_SECURITY_CHECK(L, key);
 
-	o->m_settings->setNoiseParams(key, value, false);
+	o->m_settings->setNoiseParams(key, value);
 
 	return 0;
 }