Move static methods out of TabCompleter.

Change-Id: I80df12d3494a651bc63117d26b1caf94771a51dd
Reviewed-on: http://gerrit.dmdirc.com/3862
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Update submodules: plugins (new commits)

plugins:
    9290cf3 Chris Smith <chris@dmdirc.com>
            Plugin changes for core TabCompletion updates.

            Depends-On: I80df12d3494a651bc63117d26b1caf94771a51dd
            Gerrit: http://gerrit.dmdirc.com/3863

Change-Id: Ib68ed60b448c3fee251aebe01948cc05e0cfeec3