We should use "hasObselList" property to get the URL of Obsels

[StatelessCat]

Now we supose that Obsels URL are <trace URL> + "/@obsels". Here: https://github.com/liris-tweak/samotraces.js/blob/master/src/core/KTBS.Trace.js#L37

We should get "hasObselList" instead.

If trace URL is http://www.foo.org/base1/trace1/ and this trace has

{
  ...
  "hasObselList": "@obselslist.jsonld",
  ...
}

The actual version will failed to get the Obsel list because doing GET http://www.foo.org/base1/trace1/@obsels instead of http://www.foo.org/base1/trace1/@obselslist.jsonld