DRYing up scaffold generator by generating a form partial

Creates form partial when generating a scaffold. I.e. _form.html.erb is added in addition to new.html.erb, edit.html.erb, index.html.erb, and show.html.erb. Form partial included in new and edit.

Modified form helper with sensible defaults i.e.

f.submit #value = "Create" if form's object is new_record? or "Update" if !new_record?

No need to pass in a value into a form. Helper is intelligent enough to do it for you.

Modified test.

See patch.