sent_notification.project would never be nil, and
we also have already checked message_project before
entering process_create_issue.

So we extend Gitlab::Email::Receiver for this new behaviour,
however we might want to split it into another class for better
testing it.

Another issue is that, currently it's using this to parse project
identifier:

    Gitlab::IncomingEmail.key_from_address

Which is using:

    Gitlab.config.incoming_email.address

for the receiver name. This is probably `reply` because it's used
for replying to a specific issue. We might want to introduce another
config for this, or just use `reply` instead of `incoming`.

I'll prefer to introduce a new config for this, or just change
`reply` to `incoming` because it would make sense for replying to
there, too.

The email template used in tests were copied and modified from:
`emails/valid_reply.eml` which I hope is ok.

Toggle email signup confirmation in admin settings

Implements toggling verification email #14684

See merge request !3862

Add an Event's target's title to its reference link

Given an activity feed entry like:

> Douwe Maan commented on [issue #123] at [gitlab-org/gitlab-ce]

...the `issue #123` link will now have a `title` attribute.

Plus some minor refactorings, see individual commits for details.

See merge request !4090

Disallow search engines from indexing uploads from a GitLab project.

This can sometimes include sensitive information from private projects and confidential issues. It shouldn't be indexed. Resolves #15551.

cc: @DouweM 

See merge request !4167

Use the relative url prefix for links in Wiki

Retry of gitlab-org/gitlab-ce!4026

@rymai !4050 solved all other problems how it looks like. I [tested](https://gitlab.com/artem-forks/gitlab-ce/commit/ff01eca7b559efa7cacf3412aa01cd8ae8a6db7e/builds) this with ruby22

Fixes #17071 



See merge request !4131

Add tests for unintentional filtering bug in MR

!3872 has a lack of tests for Merge Requests while !3872 has only ones for Issues.

This MR has complementary tests for MR list.

See merge request !4154

This can sometimes include sensitive information from private projects and confidential issues. It shouldn't be indexed. Resolves #15551.

Remove unused methods from Event model

These get escaped automatically.