Moved graphics classes into own namespace, added unit testing with gtest

tests/image_test/image_test.cpp

@@ -0,0 +1,9 @@
+#include "graphics/Image.hpp"
+
+#include <gtest/gtest.h>
+
+#include <optional>
+
+TEST(basic_test, Image_smokeTest_succeeds) {
+    auto im = ptprnt::graphics::Image();
+}