add framework for analysing housenumbers

This lays the groundwork for adding variants for housenumbers.
When analysis is enabled, then the 'word' field in the word table
is used as usual, so that variants can be created. There will be
only one analyser allowed which must have the fixed name
'@housenumber'.

lib-sql/tokenizer/icu_tokenizer_tables.sql

@@ -28,6 +28,10 @@ CREATE INDEX idx_word_postcodes ON word
 CREATE INDEX idx_word_full_word ON word
     USING btree(word) {{db.tablespace.address_index}}
     WHERE type = 'W';
+-- Used when inserting analyzed housenumbers (exclude old-style entries).
+CREATE INDEX idx_word_housenumbers ON word
+    USING btree(word) {{db.tablespace.address_index}}
+    WHERE type = 'H' and word is not null;
 
 GRANT SELECT ON word TO "{{config.DATABASE_WEBUSER}}";