Bug 18586: Create module to mint RDF subject URIs

Bug 18586: Create module to mint RDF subject URIs

Created the Koha::RDF module to mint URIs for RDF documents that
represent Koha bibliographic records.

_TEST PLAN_
To test the module, just run 'prove t/Koha/RDF.t'.

You'll get
some warnings about not being able to find koha-conf.xml, but
you can safely ignore them or you can point to any koha-conf.xml
file since it's not used by the test in actuality.

Signed-off-by: Magnus Enger <magnus@libriotech.no>
Works as expected. No warnings when run like:
sudo koha-shell -c "prove t/Koha/RDF.t" kohadev

Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>