Require organisation id in Annotation constructor.

[markbader]

Description:

• When calling the Annotation() constructor, an organisation_id is mandatory now. The organization_id might be provided directly within the Annotation() call, or it is inferred from current webknossos context.

Issues:

• fixes #1015

Todos:

Make sure to delete unnecessary points or to check all before merging:

• [x] Updated Changelog

[normanrz]

Not sure, I am happy with this. Providing an organization id might be cumbersome for users. And, I don't see why it wouldn't be possible to infer that upon upload. Fwiw, we could even make the dataset name optional. It could be supplied upon upload. cc @fm3