Partially addresses #47424.

In the case of spammers, we really want a hard delete to avoid retaining spam.

Closes #31021

This commit adds a number of _html columns and, with the exception of Note,
starts updating them whenever the content of their partner fields changes.

Note has a collision with the note_html attr_accessor; that will be fixed later

A background worker for clearing these cache columns is also introduced - use
`rake cache:clear` to set it off. You can clear the database or Redis caches
separately by running `rake cache:clear:db` or `rake cache:clear:redis`,
respectively.

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

Previously it was "user has already been taken", when really we were
saying the user has already been reported.

This is intended to prevent the user from creating new objects while the
transaction that removes them is being run, resulting in objects with
nil authors which can then not be edited.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/7117

Tell, Don't Ask.

This simplifies the "Report button" to not use open a dropdown and
adds a tooltip on this button.
This also removes an extra spec and adds missing specs.

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