extend word statistics to address index

Word frequency in names is not sufficient to interpolate word
frequency in the address because names of towns, states etc. are
much more frequently used than, say street names.

nominatim/api/search/query.py

@@ -102,6 +102,7 @@ class Token(ABC):
     lookup_word: str
     is_indexed: bool
 
+    addr_count: int = 1
 
     @abstractmethod
     def get_category(self) -> Tuple[str, str]: