feat(updater): unpack portable archive

Signed-off-by: Rachel Powers <508861+Ryex@users.noreply.github.com>

launcher/FileSystem.h

@@ -60,6 +60,18 @@ class FileSystemException : public ::Exception {
  */
 void write(const QString& filename, const QByteArray& data);
 
+
+/**
+ * append data to a file safely
+ */
+void appendSafe(const QString& filename, const QByteArray& data);
+
+/**
+ * append data to a file
+ */
+void append(const QString& filename, const QByteArray& data);
+
+
 /**
  * read data from a file safely\
  */