Silence two warnings

NOTE:  I don't know if these are the best fixes for these issues.  I'm happy to change to or investigate different solutions, just let me know.  It just would be really nice to not see these all the time in the "sandbox" app. :)

Silence this just for the sandbox:

    [WARNING] You are not setting Devise.secret_key within your application!
    You must set this in config/initializers/devise.rb. Here's an example:

And silence this for everything using the Spree install generator:

    [deprecated] I18n.enforce_available_locales will default to true in the future. If you really want to skip validation of your locale you can set I18n.enforce_available_locales = false to avoid this message.