feat(ui): improve info dialog before updating an instance

Adds a 'Cancel' option, and add a note about doing a backup before
updating.

Signed-off-by: flow <flowlnlnln@gmail.com>

launcher/InstanceCreationTask.h

@@ -36,6 +36,9 @@ class InstanceCreationTask : public InstanceTask {
    protected:
     void setError(QString message) { m_error_message = message; };
 
+   protected:
+    bool m_abort = false;
+
    private:
     QString m_error_message;
 };