Create "All Ages" audience

[leonardr]

A small number of classics, like "20,000 Leagues Under the Sea", are suitable for all ages. (As opposed to "Alice in Wonderland", which is generally classified solely as a children's book, even though adults can enjoy it.) Classifying these books under "Children", as frequently happens, hides them from the grown-up sections of the library. We want these books to appear in both sections.

The simplest way to do this is to add a new audience for such books and include it in lane definitions, either implicitly or explicitly.

What we really mean by "all ages" is "everyone with reading fluency", so perhaps "all ages" has a minimum age requirement of 6 or so.

While we're creating new audiences, we may also want to create a RESEARCH audience, for works that, however they were initially classified, are no longer of general interest. This will help us resolve the "obscure books from Gutenberg" issue without removing those titles altogether.