introduce constant for configuration directory

This replaces {data_dir}/settings throughout the code, so that
the configuration may be placed somewhere else in the directory
structure (e.g. in /etc).

cmake/script.tmpl

@@ -7,6 +7,7 @@ require('@CMAKE_SOURCE_DIR@/lib-php/dotenv_loader.php');
 @define('CONST_BinDir', '@CMAKE_SOURCE_DIR@/utils');
 @define('CONST_DataDir', '@CMAKE_SOURCE_DIR@');
 @define('CONST_SqlDir', '@CMAKE_SOURCE_DIR@/lib-sql');
+@define('CONST_ConfigDir', '@CMAKE_SOURCE_DIR@/settings');
 
 loadDotEnv();
 $_SERVER['NOMINATIM_NOMINATIM_TOOL'] = '@CMAKE_BINARY_DIR@/nominatim';