Add a script for importing books

Books should be in one directory, and be named <ISBN>.epub

This patch also adds an admin page for books that have been imported
that need to have metadata manually added etc.

There are two changes to the db schema:
ALTER TABLE books MODIFY COLUMN title CHAR(255) DEFAULT '';
ALTER TABLE books ADD UNIQUE (isbn);
Merge branch 'master' of https://github.com/MagnusEnger/Ebooksforlib