add library directories to config

Allows to reduce the number of parameters in functions that take
the config anyway.

nominatim/config.py

@@ -39,6 +39,16 @@ class Configuration:
             self._config['NOMINATIM_ADDRESS_LEVEL_CONFIG'] = \
                 str(config_dir / 'address-levels.json')
 
+        class _LibDirs: # pylint: disable=too-few-public-methods
+            pass
+
+        self.lib_dir = _LibDirs()
+
+    def set_libdirs(self, **kwargs):
+        """ Set paths to library functions and data.
+        """
+        for key, value in kwargs.items():
+            setattr(self.lib_dir, key, Path(value).resolve())
 
     def __getattr__(self, name):
         name = 'NOMINATIM_' + name