CLC-3783 Textbooks may include materials without an ISBN

https://jira.ets.berkeley.edu/jira/browse/CLC-3783

As you can see from the commit list, this includes many other changes as well.

* Finally support non-testext non-production-server textbooks tests.
* Improve existing tests & reactivate the choice-of-materials test.
* Add a dummy JSON for more convenient client-side development.
* Reinstate targeted links to the bookstore. (These were originally tried in https://github.com/ets-berkeley-edu/calcentral/pull/1982 but then reverted because direct links weren't loading correctly. They now work in my testing, & so we'll give them another try.)
* Changed the layout somewhat to take advantage of bookstore links, including an icon for the Cal Student Store.
@raydavis can we replace the `\u0026` everywhere with `&`?
e.g.
http://www.bkstr.com/webapp/wcs/stores/servlet/CourseMaterialsResultsView?catalogId=10001&categoryId=9604&langId=-1&courseId_1=43784267&storeId=10433&demoKey=d&orderItemStoreId=10433&purpose=browse&salesTrack=BL
does work, but with the `\u0026` it doesn't.