Bug Fix: Only set validation rules on submit

The validation rules of the contact plugin were causing issues with other forms on the same page.

This is easily prevented by setting the validation rules only when the contact form is actually submitted.

The long list of additions and deletions is due to a change in indentation, caused by splitting up one if statement into two if statements on lines 259 and 263.

This simple fix is also included in https://github.com/pyrocms/pyrocms/pull/2414, but I'd appreciate it if this could already be part of 2.2.