Add a simple unit test for widget_add_from_file()

unittest/mgos.h

@@ -0,0 +1,12 @@
+#ifndef __MGOS_H
+#define __MGOS_H
+
+#include <stdint.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+
+#include "mgos_mock.h"
+
+#endif // __MGOS_H