FrameContainers should expose a Connection.

Anywhere that doesn't just work with a Connection, cast back to a Server for
now. These can be tidied up later.

Change-Id: I02a54b0bcfaef08d5757cc015c356f9779ec0371
Depends-On: Id55c3611173be7ed79fae8f9e976996d713b8646
Reviewed-on: http://gerrit.dmdirc.com/2950
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Update submodules: plugins (new commits)

plugins:
    5138fca Chris Smith <chris@dmdirc.com>
            FrameContainers now expose Connections.

            Depends-On: I02a54b0bcfaef08d5757cc015c356f9779ec0371
            Gerrit: http://gerrit.dmdirc.com/2949

Change-Id: Ie706661b324006fe70cece9f7c986574251f8920