Added publishing functionality to Pubsubhubbub

Added the functionality of sending the alert to Pubsubhubbub.

Right now we have all the valid info only about pubsubhubbub . Will add a broker table later as and when more brokers are available.
@ptressel : actually that is needed. I want to get the host as well and then need to add the alert_id before rss. So string formatting will be needed anyways.