Find solution to Virtuoso SPARQL troubles about slinky

[amoeba]

@ThomasThelen mentioned two things to consider if we were to swap to Blazegraph:

1. Authentication: Virtuoso offers some authentication support we might lose if we switch
2. GeoSPARQL support: It looks like Blazegraph supports some spatial functionality but not quite GeoSPARQL. Not sure if this is really a problem but it's worth considering. See https://github.com/blazegraph/database/wiki/GeoSpatial.

[ThomasThelen]

An alternative to SPARQL requests is...

1. Write the turtle to disk
2. Upload the file to WebDAV
3. Let Virtuoso know to ingest the file to the graph
   More info here and here

Alternatively, we can possibly share storage between the triplifier and graph; there may be a way to let Virtuoso the path of the file on disk (you can do this with GraphDB)