autolock width, height and ratio after user sets the manually

This is the wish from BUG:460641 implemented, since I wanted to see if it was good for usability. It makes sense for this particular case, however I think it hints the interface actions as inconsistent by making some fields "react" while others don't.

The field locks after modifying the input box on rectangularConstrainWidget, unlocking must be done manually using the lock icon.