Certs - bugfix cert_whitelist output

* output after cert_whitelist -a or -d purported to be the whitelist entries
  for the requested course, but in fact were all of the entries in every
  course. This commit fixes that.
Textbooks accessibility changes

Removed image-based textbook info from XML tutorial.

Added not about accessibility and textbooks to Building a Course file.
Updated change log
Modify jquery.timeago to better support i18n

Use string interpolation instead of concatenation of prefix, content,
and suffix. This is motivated by the fact that Transifex does not accept
empty strings for translation (even when pgettext is used to provide
context).
visual styling changes to components and static pages in order to use updated icon button styling for duplicate and delete actions
adjusted unit_spec.js to reflect new HTML structure, and corrected screenreader label for delete button
Correct three typos in video documentation
updated static pages tests to reflect html element change in component.html
BLD-237: Persist speed preferences between videos.
Use subprocess.STDOUT, rather than sys.STDOUT to rebind stderr
i18n xmodule/course_module.py

LMS-1747
Update tolerance information for Numerical Input problems
Re-add .mpeg as possible video type
Eliminate unused import and gratuitous prints
Merge pull request #2230 from edx/anton/store-video-state

Persist speed preferences between videos.
Merge pull request #2286 from edx/sarina/i19-xmodules

i18n xmodule/course_module.py
Merge pull request #2281 from cpennington/fix-i18n-execute

Use subprocess.STDOUT, rather than sys.STDOUT to rebind stderr
Allow user with BetaTester role correctly use LTI. BLD-641.
Fixed flaky test for instructor command openended_post.

The submission time is serialized into json and sent to xqueue. Previously the
whole json body argument to send_to_queue() was being matched. Sometimes the
time calculated in the test would differ slightly from the time calculated in
send_to_grader() and the test would fail. This fix tests individual fields of
the body argument to mock_send_to_queue() instead.
Merge pull request #2211 from edx/oleg/beta_user_for_lti

Allow user with BetaTester role correctly use LTI. BLD-641.