Complete conversion of Test API resource to using PK instead of title.
Use file basename as PK.
Fix Test API Resource to allow proper generation of Resource URI.
Change all server side code to process test_id instead of test_title.
Fix client side code to query based on test_id.
Remove colon from "Begin Test:" button.
Merge pull request #2144 from cpauya/feature/2122-Exam-list-page

Feature/2122 exam list page
Merge branch 'nalanda-rct2' of github.com:learningequality/ka-lite into nalanda-rct2

Conflicts:
	kalite/student_testing/api_resources.py
	kalite/student_testing/urls.py
clear any preexisting logs when we initiate the update process
Update the BUILD_HASH whenever we start the server
Merge pull request #2146 from aronasorman/new_build_id_on_update

Tweaks to make the update process smoother
Finish changing over to test_id as test determiner.
add playlist navbar URL
Fix testlog fetching for test_ids.
Fix exam mode assignment for test_ids.
Fix Test lists to always return a list.
Merge pull request #2147 from rtibbles/student_test_fixes

Student test fixes
Add nav indicator to Tests nav link.
Remove nav indicator at test exam page so it doesn't point to the Practice nav link.
TODO: bootstrap css integration breaks the nav indicator and some input boxes.
TODO: Can select multiple exams to enable using the Enable Exam Mode button instead of just one active exam.