[#66] Cleaned up descriptor set usage

include/vkcv/Core.hpp

include/vkcv/DescriptorConfig.hpp

include/vkcv/Handles.hpp

projects/cmd_sync_test/src/main.cpp

projects/first_mesh/src/main.cpp

projects/first_triangle/src/main.cpp

src/vkcv/Core.cpp

src/vkcv/DescriptorConfig.cpp

src/vkcv/DescriptorManager.cpp

src/vkcv/DescriptorManager.hpp