astakos: Add email notifications recipients 

Astakos accept three lists of people who receive application
notifications, namely 'ADMINS', 'HELPDESK' and 'MANAGERS'. Then it sends
email notifications in a preconfigured way in these lists (ie. project
creation notifications are always sent to the 'HELPDESK' and 'MANAGERS'
email lists).

This pull request enable Astakos to specify explicitly the lists in which
every notification will be sent.