Remove deprecated issues_tracker and issues_tracker_id from project model

Closes #3941

See merge request !4603

Update schema.rb for most recent migrations

Fixes #18532

See merge request !4636

The schema doesn’t reflect the changes of the last 3 migrations:

* 20160610140403_remove_notification_setting_not_null_constraints.rb
* 20160610201627_migrate_users_notification_level.rb
* 20160610301627_remove_notification_level_from_users.rb

Remove counters from Pipeline navigation

* counters are heavy from UI perspective
* duplicates information from tabs below
* shows 0 for less active projects. Jumps from 0 to N constantly. 

I think we should render counters only when necessary and only for filters ( tabs on white bg ).  Exception:  issues, merge requests in top navigation as status of project popularity and action required from maintainers 


cc @grzesiek @ayufan @jschatz1 

See merge request !4617

Improve Gitlab::Auth method names

Auth.find was a very generic name for a very specific method.
Auth.find_in_gitlab_or_ldap was inaccurate in GitLab EE where it also
looks in Kerberos.


See merge request !4589

Enable Style/MultilineBlockChain rubocop style cop

Avoid multi-line chains of blocks.

See #17478.

See merge request !4349

Update brakeman from 3.2.1 to 3.3.2

Removes a few dependencies.

Changelog: https://github.com/presidentbeef/brakeman/blob/master/CHANGES

See merge request !4627