implement PipelineManager class.

config/Sources.cmake

include/vkcv/Core.hpp

include/vkcv/PipelineConfig.hpp

projects/first_triangle/src/main.cpp

src/vkcv/Core.cpp

src/vkcv/PassManager.cpp

src/vkcv/PipelineConfig.cpp

src/vkcv/PipelineManager.cpp

src/vkcv/PipelineManager.hpp