UI adjustments in Print Dialog Window

- move buttons to the bottom of the window
- use QDialogButtonBox that allows to follow platform-dependent button layout
- enlarge window size to not to crop content
- change "Close" button action from "accept" to "reject"

Signed-off-by: Andrey Zhdanov <andrjufka@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>