fix returning VoID for this YummyData test

[egonw]

See https://yummydata.org/endpoint/18/log/service_description?date=2020-08-05

[egonw]

Here is the specification: https://www.w3.org/TR/sparql11-service-description/

After a chat on Twitter with one of the lead Virtuoso developers, I learned VOS cannot help with this at this moment. So, we need to solve this at an Apache level. That could be tricky, as we need to figure out how to do the following:

1. Apache received a HTTP request for http://sparql.wikipathways.org/sparql
2. if the URL is exactly this URL and the full URL and there are no additional HTML parameters, then
   1. if the Accept: header is text/turtle, then it should return Service Description triples according to the above spec
   2. otherwise, it should redirect to http://sparql.wikipathways.org/
3. but if the URL has HTML parameters, then it should be proxied, as now in all cases

(Something like this :)