debian: add a libgrokj2k1-doc package for the Doxygen generated API docs

Add a libgrokj2k1-doc package for the Doxygen generated API docs, this
has been inspired from some messages in the logs about non installed
files, e.g.:

dh_missing: warning: usr/share/doc/GROK/html/index.html exists in debian/tmp but is not installed to anywhere