admin: Render subject of admin emails

Use the provided template variables to render not only the body of the
emails, but also the subject.

Fix apyrgio/synnefo#265
admin: Add tests for email rendering
admin: Send emails through send_admin_email

This function will assert if the request is valid, render the email and
then use the requested sender address to send it.

Fix apyrgio/synnefo#177
admin: Replace send_email with send_admin_email

Remove any email handling from the actions/views of each model, since
the `send_admin_email` utility handles these transparently.
admin: Add "From:" label in the UI
admin: Add tests for send_admin_email
Merge branch 'feature-admin-emails' into feature-admin
admin: Add stats view

This view currently has a div that holds four URLs:

* data-astakos-stats: Simple stats for the astakos service
* data-cyclades-stats: Simple stats for the cyclades service
* data-astakos-stats-details: Verbose stats for astakos service
* data-cyclades-stats-details: Verbose stats for the cyclades service

Hit any of the above URL using as X-AUTH-TOKEN the token of the user,
will return a JSON with the above stats.
admin: Include stats view in tests
admin: Remove relic template
Merge branch 'feature-admin-stats' into feature-admin
admin-ui: Add e-mail validation
admin-ui: Minor JS fixes

* Remove all the debugging printings
* Update the text of notifications
admin-ui: Improve the info displayed in the notifications
Merge branch 'feature-admin-ui-demo' into feature-admin