Impossible de supprimer le dernier dataset d'un topic

[abulte]

When using PUT /topics/{id} on a topics with existing datasets and passing datasets: [], this attribute is ignored. Thus, it's impossible to delete all datasets.

[streino]

@maudetes if you want to adopt this one, it should probably move to udata?

[maudetes]

Solving this bug is not trivial, but a workaround in the meantime would be to use new routes that will be introduced following: #52