Update to Rails 4
Use one client per thread, via a factory method, instead of a global.
Add client proxy hack so existing themes continue to work.
2809: Merge branch 'master' refs #2809

Conflicts:
	apps/workbench/Gemfile.lock
	apps/workbench/app/controllers/application_controller.rb
	apps/workbench/app/models/arvados_api_client.rb
	apps/workbench/app/models/group.rb
	apps/workbench/app/models/user.rb
	apps/workbench/app/views/layouts/application.html.erb
2809: Fix load_config so it loads in time to set passenger configs.
2809: Turn off secret_key_base by default, instead of requiring it in config.
2809: Fix whitespace.
2809: Add note about harmless warning when installing the themes_for_rails gem.
2809: Remove debug printfs, add comment explaining why so much "permit!"
2809: Add wait_for_ajax after submitting forms, to avoid race condition.
2809: Upgrade to Rails 4.1
2809: Rearrange "run API server during tests" to suit Minitest 5.
Also, use passenger instead of webrick.
2809: Remove some unnecessary sleep(0.1).
2809: Remove javascript and coffeescript boilerplate.
2809: Move coffee-rails out of :assets section to make tests thread-safe.

Otherwise, when Rails decides to build assets while running the test
suite, we get:

WARN: tilt autoloading 'coffee_script' in a non thread-safe way; explicit require 'coffee_script' suggested.
2809: Merge branch 'master' into 2809-workbench-rails4 refs #2809

Conflicts:
	apps/workbench/app/models/arvados_api_client.rb
2809: Merge branch '2809-workbench-rails4' refs #2809