SearchHandler works for tags & collections (#5)

A new problem has arisen. There's an obvious need for a "Show all books" menu option,
but I don't want it visible when all books ARE being shown.
More fixing of SearchHandler. Authors still not working. (#5)

Actually there are a lot of problems. e.g. "Kindle" collection brings up only
three books; there are more than that in mine. And then searching should be restricted
to the current list of _ids, but it's not. More investigation needed.

And then the highest priority should be doing sort-by.
Nor forgetting case-insensitivity.