"Two-factor" vs. "2-Factor"

Turn 2-factor authentication into 2 steps process. Disabled 2fa UI for ldap users since it is not supported

Remove class and id attributes from SanitizationFilter whitelist

Closes internal https://dev.gitlab.org/gitlab/gitlabhq/issues/2302

See merge request !631

Fix Firefox problems when it wants to render issuable component

Move project visibility from clone bar to repository details block for non empty project.

See merge request !1818

How to reset your root password

Added link and file correctly on Security doc.

Please review to make sure it's correct.

See merge request !1811

Added X-GitLab-Event header for web hooks

Adding quote_string to migration

See merge request !630

Fix link to the CI documentation

See merge request !627

Improved the backup documentation

See merge request !621

Use task_list gem for task lists

Task Lists can now be used in comments, and they'll render in previews. 👏

Closes internal https://dev.gitlab.org/gitlab/gitlabhq/issues/2271

See merge request !599

Revert "Allow to configure smtp and sendmail in gitlab.yml"

Add SIDEKIQ_MEMORY_KILLER_SHUTDOWN_SIGNAL env var

It looks like SIGTERM may not be enough to shut down a Sidekiq process
when its RSS has gotten too big. This change will allow us to experiment
with sending SIGKILL instead of SIGTERM to Sidekiq processes on
gitlab.com.

See merge request !1812

Remove tag duplicates

Prevention of getting this error:

```
ActiveRecord::RecordNotUnique: PG::Error: ERROR:  could not create unique index "index_tags_on_name"
DETAIL:  Key (name)=(XSS') is duplicated.
: CREATE UNIQUE INDEX  "index_tags_on_name" ON "tags"  ("name")
```

This migration fails if there are duplicates:
https://github.com/mbleigh/acts-as-taggable-on/blob/v3.5.0/db/migrate/2_add_missing_unique_indices.rb#L3

See merge request !623