More file previews

This adds previews for downloaded pdfs and code files.

![image](/uploads/9c199e91a1b4ea296c9b82a76e11038b/image.png)

![image](/uploads/17ea3869469417ee78e650ce750dbeb7/image.png)

src/filetype.cpp

@@ -41,6 +41,12 @@ FileType::~FileType() noexcept
 {
 }
 
+FileType &FileType::instance()
+{
+    static FileType _instance;
+    return _instance;
+}
+
 QMimeType FileType::mimeTypeForName(const QString &nameOrAlias) const
 {
     Q_D(const FileType);
@@ -113,4 +119,10 @@ QStringList FileType::supportedAnimatedImageFormats() const
     return d->supportedAnimatedImageFormats;
 }
 
+bool FileType::fileHasImage(const QUrl &file) const
+{
+    const auto mimeType = mimeTypeForFile(file.toString());
+    return mimeType.isValid() && supportedImageFormats().contains(mimeType.preferredSuffix());
+}
+
 #include "moc_filetype.cpp"