Implement Magazine Departments

At this point ISFDB only lets you group titles as "regular" (i.e. as opposed to "publication") series. If a title record belongs to a series, then it appears as part of that series everywhere in the ISFDB application, which is fine in most cases. However, in some cases a title may only be a part of a group of titles in one context, but not in other contexts. For example, if a title first appeared in "Analog" as a "Probability Zero" short story, it only belongs to the "Probability Zero" group of titles in the context of "Analog", but not when it is reprinted elsewhere. Currently we handle "Probability Zero" as a regular series, but it's really a "magazine department", a different type of title groupings.

We want to add "departments" as a new feature of the ISFDB application. They should have their own records and users should be able to see a list of departments appearing in each magazine series throughout its history. Once this feature has been implemented, we will convert "Probability Zero", "Shock Shorts" and various letter columns to "departments".

Note that since department information is publication-specific, it will have to be entered in the Contents section of Edit Pub just like page numbers are currently entered there.