Remove NotificationListener.

Change-Id: I63edbcc5d77c291519899c79375b6dedfc903dd6
Depends-On: I9bc5c5321065969f68bd9c5ae0e9d3a47653f713
Reviewed-on: http://gerrit.dmdirc.com/3820
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Chris Smith <chris@dmdirc.com>
Update submodules: plugins (new commits)

plugins:
    23becb9 Greg Holmes <greg@dmdirc.com>
            Reformat previous commit.

            Gerrit: http://gerrit.dmdirc.com/3821

Change-Id: I6c7820c6d7c04f23a1414ee646b40f1b0edb2004