Have the reading of available books and installed books be lazy

There is a huge cost in getting the list of books.

It reads the full conf of each book and validates it fully.

This includes constructing the backend to see if the conf and the module agree and that the module works in JSword.

Also, if the conf is not "latin-1" then it is re-read.

Much of this can be deferred.

Suggest a multi-stage initialization.