Move all NIF reading implementation to the implementation files
components/nif/node.hpp
is currently cluttered with implementations of read/post methods. These should all be moved to the currently empty cpp file. There are some more instances of this in other files in the folder.
Doing this should allow to detangle the remaining dependency mess in the reader finishing the job started by EmperorArthur and scrawl in 38bcff26 and 6b36e55a.