UI must use the service endpoint URL

Not sure if 4.5.0 or 4.6.0, feel free to bump up the version if a release is in progress, please.

I decided to test the PR for GeoSparql - https://github.com/apache/jena/pull/1204

And used the example Assembler file from https://jena.apache.org/documentation/geosparql/geosparql-assembler.html. Fuseki loaded the Assembler fine. But when I tried to query it, I realized it was getting 404 errors.

I hard-coded the `/sparql` in the UI HTTP requests, but the GeoSparql example doesn't define an endpoint. The UI must be able to derive the URL from the given configuration, instead of using a hard-coded value.

Already fixed the "Info" tab. Now going through the rest of the code to fix it