Use `tripper` for `Triplestore` and `TripleStoreConfig`

[CasperWA]

I personally wonder why the TripleStoreConfig and Triplestore-strategy itself are so tightly restricted to agraph. I think it rather makes sense to focus more on the oteapi/tripper interfacing through ontokb in order to make a generic triplestore interface. Once this is provided, this Triplestore-strategy might be confusing for a potential oteapi-user/developer in the end.

Originally posted by @MBueschelberger in #222 (comment)