Add an error message pop-up when curators try to edit metadata on empty models

[vanaukenk]

The Noctua form allows a curator to edit metadata, e.g. title, comments, and click save even if there are no individuals, i.e. the model is empty. However, the metadata doesn't actually update on the form which can be confusing for curators who might think that clicking save should update what they see.

The work here is to add an error message pop-up when curators try to edit metadata in the form before creating any annotations.

@tmushayahama - ideally the error message would pop up before curators ever make an edit and click save; that way they won't do work and then lose it.

We can paraphrase the error message that comes up in the graph editor:

"Error: The model has no individuals. Empty models cannot be saved. Please create an annotation and try again."