implement per-feed stemming language setting

schema/versions/mysql/128.sql

@@ -1,5 +1,10 @@
 BEGIN;
 
+alter table ttrss_feeds add column feed_language varchar(100);
+update ttrss_feeds set feed_language = '';
+alter table ttrss_feeds change feed_language feed_language varchar(100) not null;
+alter table ttrss_feeds alter column feed_language set default '';
+
 UPDATE ttrss_version SET schema_version = 128;
 
 COMMIT;