Rails 4.0 upgrade

Override new? method for Embedded model (Field class) because the original new? method
check the new? from the parent object, this make hard to know if the
Embedded items already exists or not in the database. Parent object (FormSection class) is responsible
to set to saved or not the embedded items.
    
Remove from field (Field class) validation the test for new? that does not make sense
because we want to make sure that when saving the FormSection even all
the "field" are new they don't introduce duplicated values. This apply as
well for existing fields.
    
Added more test cases.

Fix test edit.html.erb_spec.rb because there is a check field.new? in the edit template, so we must save the form section to render correctly.