Initial PhabricatorIRCFeedNotificationHandler

Summary:
Follows Phabricator's feed and puts notifications into channels
that are configured.

~~notification.all - bool - 1:1 stories to messages~~
notification.types - array - Specific story types to notify for - ["differential", "maniphest"]
notification.verbosity - int - Range of 0-3 for verbosity
notification.max_pages - int - Maximum number of pages to go back per poll
notification.page_size - int - Size of pages (limit) to poll
~~notification.channels - array - Array of channels to send messages to~~
~~notification.sleep - int - Seconds to sleep between polls~~

Test Plan: Run phabot with various configuration options

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin, asherkin

Differential Revision: https://secure.phabricator.com/D4418