refactor and finalize descriptor manager.

config/Sources.cmake

include/vkcv/Core.hpp

include/vkcv/DescriptorConfig.hpp

include/vkcv/DescriptorSet.hpp

projects/first_triangle/src/main.cpp

src/vkcv/Core.cpp

src/vkcv/DescriptorConfig.cpp

src/vkcv/DescriptorManager.cpp

src/vkcv/DescriptorManager.hpp