Verticall scroll navigation and fix (#200)

* Remove scroll tracking from Page component

* Replace initial scrolling trigger with initialPage prop to be more clear on when to scroll to inital page

* Add current page tracking back to HorizontalPager

* Memoize prevChapter and nextChapter functions

* Rewrite navigation in vertical pager to scroll by screen percentage instead of whole pages, refactor code

* Handle last pages explicitly to fix issue with small last pages

src/components/reader/pager/DoublePagedPager.tsx

@@ -65,7 +65,6 @@ export default function DoublePagedPager(props: IReaderProps) {
                     index={curPage}
                     src={(pagesDisplayed.current === 1) ? pages[curPage].src : ''}
                     onImageLoad={() => {}}
-                    setCurPage={setCurPage}
                     settings={settings}
                 />,
                 document.getElementById('display'),