Added reverse playlist button in playlist editor

Added the option to reverse the playlist order in the playlist editor.
Unfortunately this is quite slow on large playlists as each video animates
moving places in the playlist. Ideally for playlists larger than say,
20 items, the transition animations would be disabled and the reversing
would be done instantaneously.

playlist-editor/src/components/PlaylistEditor.svelte

@@ -10,6 +10,7 @@
   import PlaylistPlusIcon from "./icons/PlaylistPlusIcon.svelte";
   import PlusMultiple from "./icons/PlusMultiple.svelte";
   import SaveIcon from "./icons/SaveIcon.svelte";
+  import ReverseIcon from "./icons/ReverseIcon.svelte";
   import LoadingModal from "./LoadingModal.svelte";
   import Modal from "./Modal.svelte";
   import PlaylistVideo from "./PlaylistVideo.svelte";
@@ -128,6 +129,15 @@
     modalType = ModalType.Export;
   }
 
+  async function reversePlaylist() {
+    let reversed = new Array(videos.length);
+    for(let i = 0; i < videos.length; i++) {
+      let r = videos.length - i - 1;
+      reversed[i] = videos[r];
+    }
+    videos = reversed;
+  }
+
   async function savePlaylist() {
     const videoIds = videos.map((video) => video.videoId.toString());
     playlist = { ...playlist, videos: videoIds };
@@ -196,6 +206,12 @@
         <FloatingButton on:click={displayExport} title="Export videos"
           ><ClipboardMultiple /></FloatingButton
         >
+        {#if videos.length > 1}
+        <FloatingButton
+          on:click={reversePlaylist}
+          title="Reverse order"><ReverseIcon /></FloatingButton
+        >
+        {/if}
         <FloatingButton
           on:click={savePlaylist}
           title="Save the playlist"

playlist-editor/src/components/icons/ReverseIcon.svelte

@@ -0,0 +1,4 @@
+<svg style="width:24px;height:24px" viewBox="0 0 24 24">
+    <path fill="currentColor" d="M 6.164062,0 3.0644531,4.8320311 0,9.6855465 4.0312497,9.7597654 V 23.999999 H 7.9902341 V 9.8183594 L 12,9.8632814 9.1015622,4.921875 Z" />
+    <path fill="currentColor" d="M 16.03125,0 V 14.240234 L 12,14.314452 l 3.064452,4.853517 3.09961,4.83203 2.937499,-4.921874 2.898438,-4.941406 -4.009765,0.04492 V 0 Z" />
+</svg>