Mock mongo event tracking backend during tests

Add mock package to RTD requirements

Fix error encoding datetime objects in the event track logger backend

strip processed fields in instructor dash

The function json.dumps was being called with incorrect arguments,
causing an infinite recursion when serializing an event containing
datetime objects

Update discussion.md

Do not store expanded action URLs.

Fixes extra 'file' that was leftover locally after import

Adam/welcome email

Remove dogstatsd-python in favor of dogapi

They are not portable. STUD-681.

Minor updates.

fix templates

Change course id limit to 65.

Updating LTI Jasmine tests.

Due to the fact that by default the LTI settings have "http://www.example.com"
set as the default form action (launch_url), tests were updated to reflect the
fact that when setting is in default state, form is not submited, even when
the form action is not empty.

Also added datadog application to commom django apps and set it to use
a local statsd server by default.

STUD-726

Update `requests` library to 1.2.3

Improve forums nav accessibility

Add logging to save item

Add event tracking with configurable backends

Adding styles to fix issue BLD-221.