Update submodules: plugins (new commits)

plugins:
    c7a4057 Greg Holmes <greg@dmdirc.com>
            Events not listeners.

            Gerrit: http://gerrit.dmdirc.com/3785

Change-Id: I4ec2f44c9f49e36cb313966deccbb9413d6ec093
Fix @Nonnull lies.

Change-Id: I32b4a4cd7828e8c3457072b897f5f2c3e0575ca3
Reviewed-on: http://gerrit.dmdirc.com/3790
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager
Update submodules: plugins (new commits)

plugins:
    623fb97 Greg Holmes <greg@dmdirc.com>
            Fix icon/titles in treeview.

            Gerrit: http://gerrit.dmdirc.com/3789

Change-Id: I7ed14d534e0ee2edd85c137f990b3979dcb654a2