Replace documentation link with links to clients

In research we found that developers orientate themselves around the
API clients rather than the documentation.

We should get them to the client documentation as quickly as possible.

We currently link to the API documentation in three places:
- API integration page
- global footer
- template ‘API info’ page

For the first two this commit:
- removes the link to the documentation
- adds links to each of the 5 clients

For the last one it just removes the link entirely.

tests/app/main/views/test_dashboard.py

@@ -277,7 +277,6 @@ def test_menu_send_messages(mocker,
             service_id=service_one['id'],
             template_type='sms')in page
         assert url_for('main.manage_users', service_id=service_one['id']) in page
-        assert url_for('main.documentation') in page
 
         assert url_for('main.service_settings', service_id=service_one['id']) not in page
         assert url_for('main.api_keys', service_id=service_one['id']) not in page
@@ -312,7 +311,6 @@ def test_menu_manage_service(mocker,
             template_type='sms') in page
         assert url_for('main.manage_users', service_id=service_one['id']) in page
         assert url_for('main.service_settings', service_id=service_one['id']) in page
-        assert url_for('main.documentation') in page
 
         assert url_for('main.api_keys', service_id=service_one['id']) not in page
         assert url_for('main.show_all_services') not in page