Remove Online specific references:

-Remove hard-coded cart name references.
-Remove login validations from CloudUser model, login validation must be done by authentication plugin.
-Remove 'medium' gear size references
-All 'small' gear size references must be from configuration files.
-Remove stale application_observer.rb and its references
-Remove stale 'abstract' cart references
-Remove duplicate code from rest controllers
-Move all get_rest_{user,domain,app,cart} methods in RestModelHelper module.
-Cleanup unnecessary TODO/FIXME comments in broker.