Back button implementation (#47)

* Added the back button to the main Ui

* Changed the naviation in the reader ui so that when the next or previous chapter links are clicked, instead of adding the a new history entry, it will replace the current History entry and rereder the Reader component

* - Made changes so that if history is of length 1 then the backbutton will take you to /library
- made use of the startsWith method so that if we use url for the saving the last viewed category there won't be a need to change this
- changed a few relative imports to absolute imports

* Back button won't show for any route that has an icon in the  sidebar

src/components/navbar/ReaderNavBar.tsx

@@ -228,7 +228,7 @@ export default function ReaderNavBar(props: IProps) {
                             color="inherit"
                             aria-label="menu"
                             disableRipple
-                            onClick={() => history.push(`/manga/${manga.id}`)}
+                            onClick={() => history.goBack()}
                             size="large"
                         >
                             <CloseIcon />
@@ -344,6 +344,7 @@ export default function ReaderNavBar(props: IProps) {
                             {chapter.index > 1
                         && (
                             <Link
+                                replace
                                 style={{ gridArea: 'prev' }}
                                 to={`/manga/${manga.id}/chapter/${chapter.index - 1}`}
                             >
@@ -358,6 +359,7 @@ export default function ReaderNavBar(props: IProps) {
                             {chapter.index < chapter.chapterCount
                         && (
                             <Link
+                                replace
                                 style={{ gridArea: 'next' }}
                                 to={`/manga/${manga.id}/chapter/${chapter.index + 1}`}
                             >