Avoid sending empty notification digests.
paul

Conflicts:
	wiki/src/main/pages/Groups/DigestEmailMailTemplate.vm
	wiki/src/main/pages/Groups/DigestEmailSender.groovy
Callback from the activity-stream into the groovy pages to send "relevant mails" having processed the event.
paul
Merge branch 'master' of https://github.com/xclams/neaGPS