API playground example OAuthkey points to SURFnet specific configuration

[surfnet-niels]

When using the API playground, the OAuthkey provided is "https://testsp.surfconext.nl/shibboleth" However this Sp is not configured in ServiceRegistry thus breaks the oppertunity to actially test this functionality. Perhaps better to set this to teams.demo.openconext.org in coin/api/playground/ApiSettings.java as that will at least mimick OpenCoenxt Teams for a default OpenConext, or make this configurable at installtime.