Annotation review GUI

[christian-oreilly]

For collaborative annotation workflow, it is generally a good idea to have an annotation review process. Although this process could be done using the GIT diff of JSON annotations, this is obviously far from ideal. We should provide a GUI to support annotation revision. Correspondingly, we should add a field to the annotation structure for "reviewers" (i.e., idem as for the "authors" field, but to capture who reviewed the annotation, if anyone did).