Duplicate detection tweaks (take 2)

Continuing from #252

Fixed the ISBN error.

Also noticed that some items in my library were not being picked up based on the rules in the code.

Steps to reproduce:
1. Create book item. Title it `Foo Bar`.
2. Create another book item. Title is `Foo: Bar`
3. Check for duplicates. Items detected as duplicate.
4. Create a third book item. Title it `Foo Foo`
5. Check for duplicates. No duplicates found.

I tweaked the comparison function and sorted the result rows by normalized titles. Now title like `"Yes" man` and `Yes man` should also be picked up. The alternative is to compare titles with all other titles, but that is very very slow (which is probably why this was coded the way it is to start with).