Contact form: Makes the fields get sent and displayed in correct order

This PR introduces a new method that compiles the form into an array of lines that is sorted by field indexes, so that no field is out of place. Also now both the success message that shows the completed form and the email body are generated by a single method. Fixes #49 
Ouch, I have forgot about this one. Yes, I have left the blockquote tag in place here only to preserve the way the message looks on the client side.