[Bot] Split notification handler in 2 classes

The code was refactored this way so the notification messages and
policies can be easily changed.
ExtendedIRCDifferentialNotificationHandler is now a abstract class.
There are two methods that need to be implemented: processRecipients,
which deals with notification policies and processMessage, responsible
to build the message used in the notification.

Signed-off-by: Mailson Menezes <mailson.menezes@openbossa.org>
[Bot] The actor of an action shouldn't be notified

A recent refactoring introduced a bug where the actor of an action was
being notified of its own actions.

Signed-off-by: Mailson Menezes <mailson.menezes@openbossa.org>