This enforces the terms in the web application. These cases are
specced:

- Logging in: When terms are enforced, and a user logs in that has not
  accepted the terms, they are presented with the screen. They get
  directed to their customized root path afterwards.
- Signing up: After signing up, the first screen the user is presented
  with the screen to accept the terms. After they accept they are
  directed to the dashboard.
- While a session is active:
  - For a GET: The user will be directed to the terms page first,
    after they accept the terms, they will be directed to the page
    they were going to
  - For any other request: They are directed to the terms, after they
    accept the terms, they are directed back to the page they came
    from to retry the request. Any information entered would be
    persisted in localstorage and available on the page.

[ci skip]

Fix https://gitlab.com/gitlab-org/gitlab-ee/issues/4474

Conflicts:
	db/schema.rb
	ee/app/controllers/ee/admin/application_settings_controller.rb
	ee/app/helpers/ee/application_settings_helper.rb
	ee/app/models/ee/application_setting.rb
	ee/app/models/license.rb
	ee/app/views/layouts/service_desk.html.haml
	ee/app/views/notify/approved_merge_request_email.html.haml
	ee/app/views/notify/service_desk_new_note_email.text.erb
	ee/app/views/notify/service_desk_thank_you_email.text.erb
	ee/app/views/notify/unapproved_merge_request_email.html.haml
	ee/lib/ee/api/entities.rb
	ee/spec/controllers/admin/application_settings_controller_spec.rb
	ee/spec/models/application_setting_spec.rb
	ee/spec/requests/api/settings_spec.rb
	lib/api/settings.rb
	spec/mailers/previews/notify_preview.rb