Strip whitespace from isbn parameter
Add paper_trail gem.

Adding an audit log to Book in preparation for 
changes and modifications to be made by users.

Disable paper_trail in testing for now - I should 
add some tests for ensuring things are versioned.
Only lookup book metadata on create.

Ideally the automatic book metadata lookup will
move away from living in the model soon - rather
just being a helper in the new book form.

This also improves test coverage for the book
model and allows the openlibrary_id attribute
to be mass-assigned.
CSS tweaks for edit form

Align h1s and h2s more consistently across the app
Add form to edit a book

Users can change the title, author, ISBN, Google
Books ID and the Openlibrary ID.
Combine edit link and new copy link in 'actions' block
Add cancel link to edit form
Table CSS styling
Ensure paper_trail stores the changes to a model
See a history of all revisions to a book.
Add link to revision history in book actions list
Merge pull request #4 from JordanHatch/book-editing

Allow books to be edited