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.
Push out email based on the user's timezone
(Issue 878) Fix intermittent test failure when creating a tenant
(Issue 878) Remove @api private from public method
Merge branch 'issue-878' of https://github.com/mrvisser/Hilary into issue-878
Small documentation improvement
Merged master into simong/emailaggregation
(TravisCI) Manually install elasticsearch 0.90.13
Implement "Become User" functionality
Change oae-rest branch to become-user
Add indication in log when a user is impostered
(BecomeUser) Review followup
(BecomeUser) Filter HTTP headers when logging
soffice binary default is soffice not soffice.bin
Merge pull request #880 from mrvisser/travisci-elasticsearch-0.90.13

(TravisCI) Manually install elasticsearch 0.90.13
Merge pull request #881 from stuartf/soffice.what

soffice binary default is soffice not soffice.bin
Improve image JPG conversion logging
Merge pull request #875 from mrvisser/become-user

(BecomeUser) Implement "become user" functionality
Pointing oae-rest to oaeproject's github rather than mrvisser's.
Merge pull request #882 from mrvisser/improve-image-conversion-logging

Improve image JPG conversion logging