add new-style schema versions and updater

schema/versions/mysql/13.sql

@@ -0,0 +1,6 @@
+alter table ttrss_filters add column inverse bool;
+update ttrss_filters set inverse = false;
+alter table ttrss_filters change inverse inverse bool not null;
+alter table ttrss_filters alter column inverse set default false;
+
+update ttrss_version set schema_version = 13;