Resources (#1)

* start some resource fiddling

* start some resource fiddling

* initiate a real resource manager

* fix color flicker in rendering

* delete unintended constructors

and add a convenience function to reset the render-image (from the
original image, aka. clone again)

* [OpenGL deprecation warning]

The compiler said that these functions are "deprecated". They seem to
be useless anyway...

* various improvements

* add resource enumerator and documentation

* fix constness stuff

* use existing iterator for insertion

* init unit tests

* rm bogus file

---------

Co-authored-by: m-aXimilian <keuffnermax@gmail.com>

lib/imaging/PixelariumImage.hpp

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <memory>
+#include <opencv2/core/mat.hpp>
+#include <string>
+
+namespace pixelarium::imaging
+{
+class PixelariumImage
+{
+   public:
+
+    explicit PixelariumImage(const std::string& uri);
+
+    // get back the defaults
+    PixelariumImage() = default;
+    // we cannot copy an Image since this conflicts with the _img field
+    PixelariumImage(const PixelariumImage& other) = delete;
+    PixelariumImage(PixelariumImage&& other) noexcept
+        : img_(std::move(other.img_)) {}
+    // requires a copy ctor which we don't have
+    PixelariumImage& operator=(const PixelariumImage& other) = delete;
+    PixelariumImage& operator=(PixelariumImage&& other) noexcept
+    {
+        if (this != &other)
+        {
+            img_ = std::move(other.img_);
+        }
+
+        return *this;
+    }
+
+    ~PixelariumImage() = default;
+
+    const cv::Mat& GetImage() const { return *this->img_.get(); }
+
+   protected:
+    std::unique_ptr<cv::Mat> img_;
+};
+
+}  // namespace pixelarium::imaging