rename engine.hpp/cpp to Engine.hpp/cpp & move Engine, Time and mainloop classes to 'engine' folder

src/graphics/render/Decorator.cpp

@@ -14,7 +14,7 @@
 #include "objects/Players.hpp"
 #include "logic/LevelController.hpp"
 #include "util/stringutil.hpp"
-#include "engine.hpp"
+#include "engine/Engine.hpp"
 #include "files/files.hpp"
 
 namespace fs = std::filesystem;

src/graphics/render/WorldRenderer.cpp

@@ -11,7 +11,7 @@
 #include "assets/Assets.hpp"
 #include "assets/assets_util.hpp"
 #include "content/Content.hpp"
-#include "engine.hpp"
+#include "engine/Engine.hpp"
 #include "frontend/LevelFrontend.hpp"
 #include "frontend/ContentGfxCache.hpp"
 #include "items/Inventory.hpp"