Replace quiet_assets gem with sprockets-rails 3.1.0 config

[kmcphillips]

@sonalkr132 @dwradcliffe

You can rebase #1341 over this to simplify it a bit. Part of the Rails 5 upgrade.

Replaces quiet_assets with config in sprockets-rails. Bumps the sprockets-rails version to 3.1.0 to include the feature. rails/sprockets-rails#355

[dwradcliffe]

👍

[sonalkr132]

This doesn't work in rails 4 😓

[kmcphillips]

I should have waited for 4.2.7. There's a bug in ActiveSupport::Logger#silence that prevents this from also silencing the console (it silences the log file) that has been backported to 4-2-stable.

[kmcphillips]

rails/rails#25341