Partially addresses #47424.

and rubocop fixes

Send a confirmation email when the user adds a secondary email address. Utilizes the Devise `confirmable` capabilities. Issue #37385

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

In 8278b763 the default behaviour of annotation
has changes, which was causing a lot of noise in diffs. We decided in #17382
that it is better to get rid of the whole annotate gem, and instead let people
look at schema.rb for the columns in a table.

Fixes: #17382

Also:
- Get rid of legacy :strict_mode
- Get rid of custom :email validator
- Add some shared examples to spec emails validation

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Emails are used to associate commits with users. The emails
are not verified and don't have to be valid email addresses. They
are assigned on a first come, first serve basis.

Notifications are sent when an email is added.