Add OrderForm.preprocess() class method.
preprocess should be a class method, not static
Removed redundant JS on checkout page.
Remove stray print() call.
Fix and add comments.
Move variable declarations around for clarity.
Remove unused variable.
Cleaned up and enhanced docstrings/comments for the order form and its components, as well as minor refactoring of the field hiding code for readability.
Fix rendering of payment fields when checkout steps aren't split.