Provide ebook filter/count on Subject page

[George]

When you're looking at a subject, we should add a way to only show ebooks in the carousel.

So, similarly to the way you can sort Works by an author on an Author page, we should allow a way to filter books per subject.

I suggest a switch at the top of the page, like this:

Default
[SUBJECT] <b>5,345 books</b> / <a>43 eBooks</a> Published between 1923 & 2010

If eBook selected
[SUBJECT] <a>5,345 books</a> / <b>43 eBooks</b> Published between 1923 & 2010

[George (george-archive)]

Mock for Lance on new ebook filter.

[George (george-archive)]

Lance - can you mock, then pass to Edward? (Or, Anand?)

[Lance Arthur (lance-arthur)]

I added a fake link to the top of the subject page and some notes to the template to indicate what should happen when teh page loads and when the carousel/graph range changes.

[George (george-archive)]

(Anand has already begun this)