Added spec_helper and cleaned up specs. Now all specs require 'spec_help...

Added spec_helper and cleaned up specs. Now all specs require 'spec_helper'. Specs previously did not pass when run individually. They now do. spec_helper only requires gon, rabl, and jbuilder to ensure requires are consistent with use of the gon gem. Also, removed the error raising inside rabl and jbuilder methods as the Gon::Rabl and Gon::Jbuilder modules are no longer conditionally required.