Daggerify the DCC plugin.

Rename old DCCPlugin to DCCManager and inflate it using dagger.

Also remove unused method in OsdPlugin.

Change-Id: Ie8eb84b187ff9bc9379bdae41fcc4ecec85b6964
Depends-On: I99ebc7d10f558008a7889252cc3c96f39747303e
Reviewed-on: http://gerrit.dmdirc.com/2861
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>