add field to each artwork that allows criticism from curators

[slivingston]

curators that Tekuma approves should be able to leave criticism about artwork.

We need to elaborate requirements on this. E.g., should someone at Tekuma be able to moderate, edit?

relevant to issue #11

[afikanyati]

A suitable term for this could be called a Curator Appraisal.

I've realized that this feature is suitable for for collections but not artworks. Curator's wouldn't want to write an appraisal for every artwork on the database.