Merge 7.3.pre CE to EE

See merge request !177

Merge 79190fe0 (7.3.0-pre) and serialize_service_properties

This combines two merges because each individual merge breaks the build on its own.

See merge request !175

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

API MR ordering

Fixes #1477

See merge request !1076

Use sockets to connect to Redis

See merge request !1088

Fix LdapGroupLink error message

See merge request !176

Merge remote-tracking branch 'subscribers/serialize_service_properties' into merge-79190fe0-7.3.0-pre

ActiveModel::Validations has an 'errors' attribute, but no 'error'.

First I did `rake dev:setup` at 405a5acb; then `rake db:migrate` at
e93523ed.

Conflicts:
	Gemfile
	README.md
	VERSION
	db/schema.rb
	doc/install/installation.md
	lib/gitlab/git_access.rb
	lib/gitlab/ldap/user.rb
	spec/lib/gitlab/ldap/access_spec.rb

Implement comments on parallel diff

Fixes #1565

See merge request !1090

Feature oauth refactoring

See merge request !173

Fix grammatical error in 'not merged changes' msg

Update user_management.md

Adding ability to configure webhook timeout via gitlab.yml

[Refactor] Remove duplicated labels step

formatting changes, table->database

Use the default Unicorn socket backlog value: 1024

See merge request !1087

set fail_timeout=0 as recommended by Unicorn

[UX] Disable buttons if form is empty

[UX] Update tag count if tag gets deleted via web interface

set the number of workers to # of cores