Update submodules: plugins (new commits)

plugins:
    c4c7c42 Chris Smith <chris@dmdirc.com>
            Don't pass WindowManagers to FrameContainers.

            Depends-On: Iadbca8a28f7ef3372df7fda722a3cbba2a0fbad6
            Gerrit: http://gerrit.dmdirc.com/2843

Change-Id: I0fc174edadfd144dce206480b719c6e86285e8fe