Improve changelog display

Hi! And I just said I would only make minor changes... :-P

This change fixes a bug which resulted in changelogs not being displayed at all if any bracket was contained (like in an email address: Darth Vader <vader@deathstar.xyz>), but since reading a changelog was a pain in the tiny window that GPK provided, I also added a draggable area so the user can increase the space used up by the display scroll box if they want.

Screenshot of the result: