Add Assimp dependency and corresponding cmake lines; add assimpwrapper class in core/
Revert "Add Assimp dependency and corresponding cmake lines; add assimpwrapper class in core/"

This reverts commit 50ff239f9506ebea7cf2fb3e92f4ee9e7324ba9d.
Revert "Revert "Add Assimp dependency and corresponding cmake lines; add assimpwrapper class in core/""

This reverts commit adf2205cc6d4e3b01d1ba8bd4f968b98b65b79fb.