qtutils: make the error message box resizable

Add ResizeableMessageBox and use it in the critical() dialog.
This makes all error dialogs resizeable.

Closes #216

Suggested-by: @grandinj via github.com in #216
Signed-off-by: David Aguilar <davvid@gmail.com>
bookmarks: add "Open in New Window" action and hotkeys

Signed-off-by: David Aguilar <davvid@gmail.com>