Add alt text to emoji images

Closes #151

DiscordChatExporter.Core/Resources/ExportTemplates/HtmlShared/Main.html

@@ -195,7 +195,7 @@
                         <div class="chatlog__reactions">
                             {{~ for reaction in message.Reactions ~}}
                                 <div class="chatlog__reaction">
-                                    <img class="emoji emoji--small" title="{{ reaction.Emoji.Name }}" src="{{ reaction.Emoji.ImageUrl }}" />
+                                    <img class="emoji emoji--small" alt="{{ reaction.Emoji.Name }}" title="{{ reaction.Emoji.Name }}" src="{{ reaction.Emoji.ImageUrl }}" />
                                     <span class="chatlog__reaction-count">{{ reaction.Count }}</span>
                                 </div>
                             {{~ end ~}}

DiscordChatExporter.Core/Services/ExportService.TemplateModel.cs

@@ -210,7 +210,7 @@ namespace DiscordChatExporter.Core.Services
                             ? "emoji--large"
                             : null;
 
-                        buffer.Append($"<img class=\"emoji {jumboableCssClass}\" title=\"{emojiNode.Name}\" src=\"{emojiImageUrl}\" />");
+                        buffer.Append($"<img class=\"emoji {jumboableCssClass}\" alt=\"{emojiNode.Name}\" title=\"{emojiNode.Name}\" src=\"{emojiImageUrl}\" />");
                     }
 
                     else if (node is LinkNode linkNode)