Permit copying certificate details
I had a certificate error today and was not even able to select the text to copy it. Ended up taking a screenshot of the details.
Ideally, there should be a copy button in error dialogues (IIRC it's there for stack traces?). If this is a GTK problem, the copy button could be used as a workaround.
(Speaking of errors...can we please do away with modal dialogues for error messages entirely?)