Board alerts are checked on schedule

The Job board alerts job checks every active alert whose next check is due, asks each of its boards through the board connection, records the new matches with a score, and tells the alert's owner.

• A connection with a feed address (JSON or RSS) is asked through it.
• A connection whose address is sandbox: answers from the alert's own words, to try it end to end.
• Partner APIs of individual boards need an agreement and credentials with that board and are not built in; an alert on such a board says no connector.