provide a warning if fields are empty in dataset uploading

[mfeurer]

[mfeurer]

@ArlindKadra do you think we could add this by checking that the description (and other strings) provided by the user are not empty?

[ArlindKadra]

@mfeurer depends, momentarily we have 2 ways in which OpenMLDataset can be created. We are already enforcing certain dataset fields from the datasets/functions way, on the other hand a straight object creation would make sense to provide that. In my opinion this should be firstly done server side, a dataset can still be uploaded only with name, description, and data format.