Added wait for JavaScript when navigating to textbook page

To fix this issue:

https://jenkins.testeng.edx.org/job/edx-all-tests-auto-master/275/SHARD=3,TEST_SUITE=cms-acceptance/testReport/junit/CMS/Textbooks%20_%20No%20textbooks/When_I_go_to_the_textbooks_page/

@singingwolfboy