(class certification rejected for parties that borrowed money and claimed that "predatory lending" schemes subjected them to "toxic" adjustable-rate mortgage loans that were then bundled and sold as investments on secondary market as "mortgage-backed securities"; claims involved alleged violations of Racketeer Influenced and Corrupt Organizations Act (RICO) and unfair competition; claimed involved unconscionable increase in borrowers' debt burden because loans offered interest-only payments or minimum monthly payments at less than amount that would cover interest; court found dissimilarities in purported class members' cases such that class could not be certified; RICO and unfair competition claims fail due to lack of "common course of conduct" - loans made through many independent brokers that had no contact with Countrywide Financial).