Inject the EventBus into plugins.

Swing UI + Apple is too tangled up to do it using nice DI atm :(

Change-Id: Ie06dc705e78b6475cda01cfc1850dcb732ebcdcc
Reviewed-on: http://gerrit.dmdirc.com/2957
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>