Feature/cdodge/pylint cleanup

Initial implementation of htmlbook.

Make numeric response handle plus sign exponential correctly

delete_item should update the parent's list of children to reflect the d...

NumericResponse was failing to accept as correct an answer with a plus
sign in the exponential. For example: 5.0e+1 was marked as incorrect
if the answer was 50. However, 5.0e1 was marked as correct. This
caused confusion, since the answer shown to students included the plus
sign.

LMS Lighthouse [#242]

Add the ability to hide correctness markers

Fix/cdodge/performance optimize comment client use jumpto

delete_item should update the parent's list of children to reflect the delete operation. Also added unit test

Specify that mitx should use ruby 1.9.3-p374 for consistancy with prod

Update of Delft logo (lighthouse ticket #234)

with a custom message for when they submit something.

optimize forum page rendering as we don't pre-compute the link urls to inline discussions. We can use jump_to urls and then figure out the link path if/when end-user clicks on it. This saves a lot of unnecessary round trips to the DB as path computation is expensive, especially when it being done for every discussion module in a course in a loop.

Fixed undefined variable error in choicegroup.html

Set grading policy to an empty dict if it can't be decoded from json

Need to trigger invalid instead of error, after changes for new version ...

Fix lettuce tests so all studio ones are working and faster

Add datadog metrics capture around heartbeat timing

Fix lettuce tests to work with phantomJS