Improve cross browser compatibility

 * Do not use `instanceof' for HTMLElement
Fix key handling is conflicting with pixiv's
Improve layout performance
Change popup status while submitting bookmark form
Fix bookmark_submit keybind
[Test] Implement bookmark-mode keybind test
Change default value for conf.key.popup_illust_page_{up,down}
Fix illust.answered flag
[Test] Implement survey keybind tests