Adding 'lead' category

There were changes for [AGPUSH-432](https://issues.jboss.org/browse/AGPUSH-432) that now require a "lead" category. 

This PR adds it, so that iOS clients are also notifed when a new lead is send out


Done for [AGPUSH-449](https://issues.jboss.org/browse/AGPUSH-449)