recommended for C++ libraries

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

Add the missing Build-Depends-Package field to
debian/libgrokj2k1.symbols as suggested by lintian:

I: libgrokj2k1: symbols-file-missing-build-depends-package-field