Making the app useable with only sandbox ct keys

A big hurdle to developers getting Crowdhoster up and running was the need to get production Crowdtilt API keys before the app could even be initialized.  No longer!  Now the app will work completely with just a set of sandbox credentials provided in the .env file.  A new admin screen for setting up the production payment processor has been added, which for now just asks for a set of production Crowdtilt API keys.  Until the payment processor has been set up, campaigns cannot be promoted to production payments.

We've also made the warning messages that a campaign is in sandbox mode more prominent so no users will be confused!