Use the event bus for ClientOpened events.

Add Guava as a build-time dependency for plugins.

Change-Id: Ice5066f8c188b55f14af8ffcb38a5d5a244523b5
Reviewed-on: http://gerrit.dmdirc.com/2959
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager