This is standard for KDE dialogs, but we weren't super consistent about
it. Most of this is porting to DialogButtonBox, and using buttonRole. I
also made sure the close button is hidden in cases where we have a
cancel button already.
I also took the time to clean out some cruft like manually calling
close() and such. I probably missed a lot more spots, but this is a good
improvement.
Use the forget function to leave a room everywhere this is both for consistency and to reduce dependencies. This way no dependency on RoomManager is required to leave a room and since in all cases they have an object they can just call the function.
