Fix mime type for .htm and .html files

The code forces text/html for .shtml files, but if .html ones were used,
it would look up in the mime database and come up with application/x-extension-html

Web browsers try downloading that instead of rendering it.

libraries/embedded-webserver/src/HTTPManager.cpp

@@ -168,7 +168,8 @@ bool HTTPManager::handleHTTPRequest(HTTPConnection* connection, const QUrl& url,
 
             // if this is an shtml file just make the MIME type match HTML so browsers aren't confused
             // otherwise use the mimeDatabase to look it up
-            auto mimeType = localFileInfo.suffix() == "shtml"
+            auto suffix = localFileInfo.suffix();
+            auto mimeType = (suffix == "shtml" || suffix == "html" || suffix == "htm")
                 ? QString { "text/html" }
                 : mimeDatabase.mimeTypeForFile(filePath).name();