implement multiple rule/action filters

classes/dlg.php

classes/opml.php

classes/pref/filters.php

classes/pref/labels.php

include/functions.php

include/rssfuncs.php

js/functions.js

js/prefs.js

schema/ttrss_schema_mysql.sql

schema/ttrss_schema_pgsql.sql

schema/versions/mysql/96.sql

schema/versions/pgsql/96.sql

tt-rss.css

update.php