Inspection fixes.

Change-Id: Ia00bd92064e27c5de0493b7377cf41b9541532b8
Reviewed-on: http://gerrit.dmdirc.com/3961
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Pull out non-prefix functionality.

Move mode-only functionality into ModeManager, which can then
be used for other types of modes.

Change-Id: I8309a2f235f70c7a101266744995efcce24e9c1d
Reviewed-on: http://gerrit.dmdirc.com/3962
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>