Add automatic email notifications

The WPISuite server can now send email notifications to users when requested
from the client through the standard REST API. A field to configure a
per-project Gmail account to send from was also added.

Anything in Janeway can send an email notification just by specifying a message
and a list of users, without either having a hardcoded password in client code
(only the admin might know the password) or a locally running MTA.

Change-Id: I3dcbc80d5dea6fddcf15c480369b56047b745db9

Add email notifications

Assuming the email account has been configured for the project, email
notifications are now sent to any users assigned to task when any field
changes.  The email message includes a nicely formatted report of what
changed.

Change-Id: I06a94133fa663d0001b4e7f7dd937fd70570a8db