Make Bioassays and Bioassay sets annotatable

[Johan Vallon-Christersson]

Bioassays are currently not annotatable. It would, however, be convenient if they were. For example, bioassays represent data in a specific stage of analysis. To be able to annotate bioassays, manually or via plugins, to indicate a current state, e.g. classification group, quality bin, and so on, is desirable. These annotations could for one thing be used as input for subsequent analysis and selections. The reasoning goes for Bioassay sets.

[Nicklas Nordborg]

(In [2892]) Fixes #403: Make Bioassays and Bioassay sets annotatable