Refactored Railtie & fixed some onboarding procedures

Railtie is now split into two different modules: Default & Onboarding.
Ecrire::Railtie tries to connect to the database using Dir.pwd + '/secrets.yml'
If it fails, Ecrire assume that your blog is not
configured (Unless you're in production environment) The onboarding
procedure now generate a secret_key_base once everything is configured