#346 Add support for ghostwriters

[Ahasuerus]

Books that are ghostwritten are currently only displayed on the ghostwriter's Summary Page. For example, Andrew Niederman has written over 60 books as "V. C. Andrews" after the latter's death. Many ISFDB users have no easy way of knowing which books may have been ghostwritten and when they look at an author's Summary Page, there is no indication that there may be other books that have appeared under that author's name.

Ideally, we would display ghostwritten books both on the ghostwriter's Summary Page and on the credited author's Summary Page and also make it clear what the nature of each author's contribution is. Note that this enhancement will not affect uncredited collaborations, which are already handled correctly by the software.