Partially fix documentation translation generation

Partially fix documentation translation generation

- generate Texinfo skeletons with @translationof;

- do not copy any file besides GNUmakefile and Texinfo skeletons into
new language directories -- for each such file, either it is common to
all languages or it needs to be translated, thus in either case it
should not be copied into the new language directory;

- do not create directories for nuts, they can be created later using
TRANSLATION_DIRS=newdir new-lang.