Copy Config from gpu-screen-recorder-gtk, make it more modern and efficient with string_view and variant, use string_view in gsr info parsing

include/gui/Button.hpp

@@ -24,7 +24,6 @@ namespace gsr {
     private:
         mgl::vec2f size;
         mgl::Color bg_color;
-        bool mouse_inside = false;
         mgl::Text text;
     };
 }

include/gui/Utils.hpp

@@ -3,6 +3,9 @@
 #include <mglpp/system/vec.hpp>
 #include <mglpp/graphics/Color.hpp>
 
+#include <functional>
+#include <string_view>
+
 namespace mgl {
     class Window;
 }