Bug 29845: add classes to overdrive results action buttons

Bug 29845: add classes to overdrive results action buttons

To test:
1. You must have OverDrive credentials populated in the OverDrive
   system preferences
2. Go to the Overdrive results page and make sure you are logged in.
3. Use your browsers dev tools to look at the check-in, check-out,
   place hold, cancel hold buttons, none of them contain classes.
4. Apply patch
5. Repeat 3 again but this time they should all contain a class which
   makes them much easier to style.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>