Load remote sources when select changes or by URL

When the user select an entry from "Catalog of Services" query the
remote endpoint for remote sources and load them into "Data Repository"
field in Search Criteria Section. Also disable the URL field.

If the user fill URL field and the URL is valid, query the remote
endpoint for remote sources and also load them into "Data Repository"
select.
Merge pull request #15 from juanluisrp/update-remote-repositories

Load remote sources when select Catalog of Services changes or the user writes the URL