Replace specialist with editor

[bruvellu]

Specialist carries a strong meaning from our previous version. It is a person who is a specialist on a specific taxon. In the new version, we moved the names of these specialists to a new acknowledgement field. A specialist now is someone involved in the publishing workflow between authors and curators. The original meaning is lost, and it also precludes users from providing suggestions or small corrections to media which they are not specialists. One solution to overcome that is to convert specialist into editor, which is a more operational definition. The original specialist definition can be implemented as a separate and solely informational relationship between Taxon and Person models.

[castilhovirginia]

"editor" or "content editor"? I think content editor is better.

[bruvellu]

Using editor as a shortname and content editor as a description. I created the specialist-to-editor branch to apply these updates. It is a fairly complex change to the codebase (many views and templates refer to specialists) and I'll need to do several database and data migrations to get everything in order. For now, I've replaced specialist for editor everywhere in the code. Editor is now defined as a Person who is neither an Author nor a Curator of a particular curation, but that has some privilege in editing contents.

[bruvellu]

This is now deployed. See PR #362 for changes. Needs test to check for issues before deleting the old specialist field.