Add RDF

[jyutzler]

I was asked to produce some RDF for GeoPackage in conjunction with conceptual model activity. Since GeoPackage now aligns to this standard, it seemed sensible to make RDF for this standard and import it. It can sit next to the other schemas.

[joanma747]

In the previous version we had a JSON-LD version that produced some nice RDF. We were not sure there was a use case for it so we discontinued. We could revive it if there is a need to.

[jyutzler]

I saw that but I think it would be easier to start from scratch. Part of the reason is that there is prior work that can be brought in (i.e., GeoSPARQL) rather than starting from a blank page.
You can track my progress at https://github.com/jyutzler/geopackage/blob/conceptual-model/spec/conceptual-model/RDF/tms/tms.ttl.