Debugger: Make also individual formats persistent

I am not fully convinced this is a good idea, but it looks like
the different behaviour of type formats and individual formats
is unexpected.

Task-number: QTCREATORBUG-7412
Change-Id: I5aae39939dfe75b3d9ff6c1025bd3d9c9222695a
Reviewed-by: David Schulz <david.schulz@digia.com>