Modifications to GuidesController

# What's New?

 * Removed root element POST params in #create (How did that get there...?)
 * Using Mutations instead of strong params in #create
 * Moved duplicate code in controller and mutation into helper methods

# What's Next?

 * Setup ENV vars on staging server
 * Everything else that I listed in #178
Indent access modifiers like `protected`.<br>Keep a blank line before and after `protected`.