Extension:Echo/echo subscription table

Schema
mysql> describe echo_email_batch; ++-+--+-+-+---+ ++-+--+-+-+---+ ++-+--+-+-+---+
 * Field             | Type                | Null | Key | Default | Extra |
 * sub_user          | int(10) unsigned    | NO   | MUL | NULL    |       |
 * sub_event_type    | varbinary(64)       | NO   |     | NULL    |       |
 * sub_page_namespace | int(10) unsigned   | YES  | MUL | NULL    |       |
 * sub_page_title    | varbinary(255)      | YES  |     | NULL    |       |
 * sub_notify_type   | varbinary(64)       | NO   |     | NULL    |       |
 * sub_enabled       | tinyint(1) unsigned | NO   |     | 1       |       |