Verify schema compliance on books collection read/write

[amyjko]

While TypeScript prevents a lot of issues with schema compliance, there are a number of ways that malformed book/edition metadata might sneak into the database:

• Schema changes that aren't correctly propagated to production data
• Future functionality that imports books

We use AJV to do schema validation when compiling books; we should do the same each time we read a book for display and before we write a book for display.