Make the DMN Runner not depend on the optional locationURI attribute of DMN files anymore

[tiagobento]

DMN Runner is depending on the @_locationURI of imports to detect dependent DMNs to send to JIT Executor. We need to refactor that, and start depending on the @_namespace instead. This is probably a good invitation for a more robust Shared Worker that will maintain live copies of all DMNs inside the workspace.

[gitgabrio]

See #1383
@yesamer