Fix misleading comment
Remove the email subject prefix

This changes email subjects from:

    GitLab | Team / Project | Note for issue #1234

to:

    Team / Project | Note for issue #1234

Rationale:

* Emails should be as meaningful as possible, and emphasize content over
chrome. The "GitLab" name is more chrome than content.

* Users can tell an email coming from GitLab by the sender or the header
in the email content.

* An organization that works mainly with GitLab knows that
every SVC email comes from GitLab. For these organizations, having
"GitLab" in front of every email is just noise hiding the meaningful
information.
Don't write the project namespace in email subjects

For instance, the email "Subject" field changes from:

    Mattt / Ground Control | Saving issue doesn't work sometimes (#1234)

to:

    Ground Control | Saving issue doesn't work sometimes (#1234)

Rationale:

* Most people are receiving email notifications about a single fork:
the project activity, issues and merge requests are happening either
in a root repository or in a fork, but less often in several forks.

* It removes noise from the email subject. The namespace of the project
can still be read in the email body.

* For Entreprise users that have a single namespace "MyEntreprise",
having this repeated in every email subject is very noisy.
Write the issue/merge request title in the notification email subject

This changes the email subjects for issues and merge request
notifications from:

    Team / Project | Note for issue #1234

to:

    Team / Project | Saving issue doesn't work sometimes (#1234)

Rationale:

* Scan the subject of the email notification more easily when catching
up with a lot of notifications. Instead of having to open the email to
get the title of the issue or merge request, one can simply read the
subject of the email.

* Group messages by subject: email clients will group emails in threads
if they have the same subject.
Send emails from the author

This changes the email "From" field from "gitlab@example.com" to either:

* "John Doe <gitlab@example.com>" if the author of the action is known,
* "GitLab <gitlab@example.com>" otherwise.

Rationale: this allow mails to appear as if they were sent by the
author. It appears in the mailbox more like a real discussion between
the sender and the receiver ("John sent: we should refactor this") and
less like a robot notifying about something.
 Merge branch 'cleaner-email-headers' into 'master'

Cleaner headers in Notification Emails

Make the informations available in the notification email headers (sender, recipient, subject, etc.) more readable and meaningful.

* Remove the email subject prefix
* Don't write the project namespace in email subjects
* Write the issue/merge request title in the notification email subject
* Make the email appear as sent from the action author (the actual email address is still `gitlab@gitlab.com`)

For instance, this is the notification email for a new issue comment before:

> From: gitlab@gitlab.com
> To: myemailaddress@gmail.com
> Subject: GitLab | GitLab HQ / GitLab-Shell | New note for issue #1234

And after :

> From: Nick Brown &lt;gitlab@gitlab.com&gt;
> To: myemailaddress@gmail.com
> Subject: GitLab-Shell |  Add local update hook  (#1234)

The recipient of the notification can easily get the gist of the message without even opening it — just by looking at how it appears in her inbox. None of the actual email addresses (From, To, Reply-to) changes, just the display name.

Having a consistent subject for all notification emails sent about some resource also allow good email clients to group the discussion by thread (although grouping in Mail.app still needs some work).