Create Device model
Add test helper method for using paper_trail
Fix borrow copy link method
Show message when no revision history available for a book.
Add 'recently loaned' scope to Loan model

Loans which are active, sorted by recent first
Add recent loans to start page

Remove the "Browse the library" section and replace
with a new full-width list of the most recent loans.
Change association copy/book to  polymorphic
Remove find_by_book_reference
Devices can now have copies
Adapting UI to devices
Improving grids rendering for devices
Merge remote-tracking branch 'jordan/master'