Warn user if uuid is not passed to the data package creator

[cpina]

schema-collaboration launches data package creator UI with the uuid parameter and source parameters:

https://carles.eu.pythonanywhere.com/static/datapackage-ui/index.html?load=e1138a06-05fa-4261-9220-eb58139937f4&source=/management/

If they don't exist the behaviour is undefined. Currently data package creator UI is not giving any user feedback but in the Javascript console there are exceptions and network requests like:
GET https://carles.eu.pythonanywhere.com/api/datapackage/null/
PUT https://carles.eu.pythonanywhere.com/api/datapackage/null/

From schema-collaboration the datapackage-ui should never be called without uuid/source. But if it does (bug in schema-collaboration or a user changing the URL) it should probably fail earlier or give a notification.