[HTML] Show "Click to see attachment" on replies to attachment or embed messages without content

Closes #634

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

@@ -1,6 +1,7 @@
 @using System
 @using System.Linq
 @using System.Threading.Tasks
+@using DiscordChatExporter.Core.Exporting.Writers.Html;
 
 @namespace DiscordChatExporter.Core.Exporting.Writers.Html
 @inherits MiniRazor.TemplateBase<MessageGroupTemplateContext>
@@ -61,6 +62,10 @@
                         {
                             @Raw(FormatEmbedMarkdown(Model.MessageGroup.ReferencedMessage.Content))
                         }
+                        else if (Model.MessageGroup.ReferencedMessage.Attachments.Any() || Model.MessageGroup.ReferencedMessage.Embeds.Any())
+                        {
+                            <em>Click to see attachment</em> <span>🖼️</span>
+                        }
                         else
                         {
                             <em>Click to see original message</em>

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

@@ -1,4 +1,6 @@
-@namespace DiscordChatExporter.Core.Exporting.Writers.Html
+@using DiscordChatExporter.Core.Exporting.Writers.Html;
+
+@namespace DiscordChatExporter.Core.Exporting.Writers.Html
 @inherits MiniRazor.TemplateBase<PostambleTemplateContext>
 
 @{/* Close elements opened by preamble */}

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

@@ -1,5 +1,6 @@
 @using System
 @using System.Threading.Tasks
+@using DiscordChatExporter.Core.Exporting.Writers.Html;
 
 @namespace DiscordChatExporter.Core.Exporting.Writers.Html
 @inherits MiniRazor.TemplateBase<PreambleTemplateContext>