Render YouTube iframe for applicable video embeds (#607)

DiscordChatExporter.Core/Exporting/Writers/Html/Core.css

@@ -458,6 +458,10 @@ img {
     border-radius: 3px;
 }
 
+.chatlog__embed-youtube-container {
+    margin-top: 0.6em;
+}
+
 .chatlog__embed-image-container {
     margin-top: 0.6em;
 }

DiscordChatExporter.Core/Exporting/Writers/Html/MessageGroupTemplate.cshtml

@@ -214,8 +214,19 @@
                                             }
                                         </div>
                                     }
+                                    @if (!string.IsNullOrWhiteSpace(embed.Url) && embed.Url.IndexOf("youtube.com/watch?v=") != -1)
+                                    {
 
-                                    @if (!string.IsNullOrWhiteSpace(embed.Description))
+                                        if (embed.Thumbnail is not null && !string.IsNullOrWhiteSpace(embed.Thumbnail.Url))
+                                        {
+                                            <div class="chatlog__embed-youtube-container">
+                                                <iframe class="chatlog__embed-youtube" width="400" height="225" frameBorder="0" style="border-radius: 5px"
+                                                        src="@embed.Url.Replace("/watch?v=", "/embed/")">
+                                                </iframe>
+                                            </div>
+                                        }
+                                    }
+                                    else if (!string.IsNullOrWhiteSpace(embed.Description))
                                     {
                                         <div class="chatlog__embed-description">
                                             <div class="markdown preserve-whitespace">@Raw(FormatEmbedMarkdown(embed.Description))</div>
@@ -250,6 +261,8 @@
                                 </div>
 
                                 @if (embed.Thumbnail is not null && !string.IsNullOrWhiteSpace(embed.Thumbnail.Url))
+                                {
+                                    if (string.IsNullOrWhiteSpace(embed.Url) || embed.Url.IndexOf("youtube.com/watch?v=") == -1)
                                     {
                                         <div class="chatlog__embed-thumbnail-container">
                                             <a class="chatlog__embed-thumbnail-link" href="@await ResolveUrlAsync(embed.Thumbnail.ProxyUrl ?? embed.Thumbnail.Url)">
@@ -257,6 +270,7 @@
                                             </a>
                                         </div>
                                     }
+                                }
                             </div>
 
                             @if (embed.Image is not null && !string.IsNullOrWhiteSpace(embed.Image.Url))