add rpc method to export feedbrowser data; update schema

schema/versions/mysql/84.sql

@@ -1,6 +1,7 @@
 begin;
 
 create table ttrss_linked_instances (id integer not null primary key auto_increment,
+	last_connected timestamp not null,
 	access_key varchar(250) not null,
 	access_url text not null) TYPE=InnoDB DEFAULT CHARSET=UTF8;