added resources and their loading

resources/images/cannon.png

resources/images/collision.png

resources/images/enemy1.png

resources/images/enemy2.png

resources/images/missile.png

src/CMakeLists.txt

src/game/renderer/CMakeLists.txt

src/game/renderer/abstract_renderer.h

src/game/renderer/sdl_renderer.cpp

src/game/renderer/sdl_renderer.h

src/game/renderer/sdl_resources.cpp

src/game/renderer/sdl_resources.h