remove redundant '/manga' prefix from paths

We needed the prefix to distinguish anime paths from manga paths,
now that anime is no more, the redundancy shall be purged.

src/App.tsx

@@ -127,7 +127,7 @@ export default function App() {
                                 <Route path="/sources/:sourceId/search/">
                                     <SearchSingle />
                                 </Route>
-                                <Route path="/manga/extensions">
+                                <Route path="/extensions">
                                     <MangaExtensions />
                                 </Route>
                                 <Route path="/sources/:sourceId/popular/">
@@ -139,10 +139,10 @@ export default function App() {
                                 <Route path="/sources/:sourceId/configure/">
                                     <SourceConfigure />
                                 </Route>
-                                <Route path="/manga/sources">
+                                <Route path="/sources">
                                     <MangaSources />
                                 </Route>
-                                <Route path="/manga/downloads">
+                                <Route path="/downloads">
                                     <DownloadQueue />
                                 </Route>
                                 <Route path="/manga/:mangaId/chapter/:chapterNum">

src/components/navbar/NavBar.tsx

@@ -50,15 +50,15 @@ const navbarItems: Array<NavbarItem> = [
         title: 'Updates',
         IconComponent: NewReleasesIcon,
     }, {
-        path: '/manga/extensions',
+        path: '/extensions',
         title: 'Extensions',
         IconComponent: ExtensionIcon,
     }, {
-        path: '/manga/sources',
+        path: '/sources',
         title: 'Sources',
         IconComponent: ExploreIcon,
     }, {
-        path: '/manga/downloads',
+        path: '/downloads',
         title: 'Manga Download Queue',
         IconComponent: GetAppIcon,
     }, {

src/screens/manga/Browse.tsx

@@ -0,0 +1,12 @@
+/*
+ * Copyright (C) Contributors to the Suwayomi project
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+import React, { useContext, useEffect, useState } from 'react';
+
+export default function Browse() {
+    return <h1>fek</h1>;
+}