Add a Double Page Viewer (#105)

* add double page reader

* implement singleRTL

* add on image load handler

* add retry display time interval

* remove comments

* add double page wrapper

* fix image getting out of bounds

* remove comments

* remove unused styles

* return imageStyle as type CSSProperties

* rename DoublePagedReader to DoublePagedPager

webUI/react/src/components/manga/reader/pager/VerticalPager.tsx

@@ -114,6 +114,7 @@ export default function VerticalReader(props: IReaderProps) {
                         key={page.index}
                         index={page.index}
                         src={page.src}
+                        onImageLoad={() => {}}
                         setCurPage={setCurPage}
                         settings={settings}
                         ref={(e:HTMLDivElement) => { pagesRef.current[page.index] = e; }}