Let server come up without balanced_api_key_secret configuration

When someone is starting the app for the first time (like running
"rails console"), the server must be able to come up to let the user to
run commands without defining configuration for Balanced.
Define Configuration.[] on dummy app
Merge pull request #6 from neighborly/im-warn-blank-balanced_api_key_secret

Let server come up without balanced_api_key_secret configuration