Email Aggregation

Rather than sending out an e-mail per activity, mails will be aggregated with other emails that have ocurred recently.

This work adds an `emailPreference` field for each user where they can select how they want their email delivered.
 * Never
 * Daily
 * Immediate (with a 10 minute delay to let it aggregate with other activities in those 10 minutes)

The emails are now also internationalizable by virtue of re-using the 3akai-ux template macro's and UI bundles.