Tidy up core plugin functionality.

Move stuff from ClientModule into a CorePluginHelper, and
move CorePluginExtractor into the plugins package.

Change-Id: I0f0211edba8e8c19857d0a783f23b90aee89e84c
Reviewed-on: http://gerrit.dmdirc.com/3748
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager
Add frame changed events, deprecate listener.

Change-Id: I1d3f667790a1daedd736e46751ee8d7106d316a1
Reviewed-on: http://gerrit.dmdirc.com/3749
Reviewed-by: Chris Smith <chris@dmdirc.com>
Automatic-Compile: DMDirc Build Manager
Update submodules: plugins (new commits)

plugins:
    891ac21 Chris Smith <chris@dmdirc.com>
            Deal with core class renaming.

            Depends-On: I0f0211edba8e8c19857d0a783f23b90aee89e84c
            Gerrit: http://gerrit.dmdirc.com/3750

Change-Id: I3a9fbebe184624bd139142ad0a06dceb6dcad102