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/utilities/SpdLogger.hpp

@@ -17,10 +17,11 @@ class SpdLogger : public ILog
     void Debug(const std::string& msg) override;
     void Warn(const std::string& msg) override;
     void Error(const std::string& msg) override;
+    void ChangeLevel(LogLevel lvl) override;
 
    private:
-    std::shared_ptr<spdlog::logger> _logger;
-    std::string _file;
-    std::string _name;
+    std::shared_ptr<spdlog::logger> logger_;
+    std::string file_;
+    std::string name_;
 };
-}  // namespace pixelarium::utils::log
+}  // namespace pixelarium::utils::log