DRYed the Feed model a bit.
DRYed the Feed model a bit.

The code that checks if a feed already is in the database, before subscribing a user to it, has been moved to its own method.

jmwenda/feedbunch,amatriain/feedbunch,jmwenda/feedbunch,amatriain/feedbunch,amatriain/feedbunch,amatriain/feedbunch,jmwenda/feedbunch