Bulk set categorical field values

[M-C-McGrath]

There should be a way to set all documents to have a certain value for a specified categorical field. Both the frontend and backend are needed for this. The user interface needs to collect the following values-

• Document type (which determines which categorical fields to show)
• Field to set
• Value to set to (or if it should be cleared entirely)

Eventually we may want to support bulk setting of documents matching search values or bulk deletion, but for now let's just provide this to set/unset values for all documents.

[M-C-McGrath]

This could also potentially be a Catalyst method (I will probably treat it as such on the backend since it fits well with the Catalyst structure), but is a bit unusual in that it may be something where people want the output to go to an existing field. Which I suppose may be true for other Catalyst methods too. So we should think about how to structure things UI-wise.