Update discussion.md

- fixed typo
- roles 'moderator' and 'administrator' are explained as bullet points.
Change course id limit to 65.

STUD-726
Remove dogstatsd-python in favor of dogapi

Also added datadog application to commom django apps and set it to use
a local statsd server by default.
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.
Merge pull request #943 from edx/valera/update_lti_tests

Updating LTI Jasmine tests.
Merge pull request #928 from edx/christina/courseid_length

Change course id limit to 65.
change formatting for email messages to use full_name instead of first_ and last_name

fix templates
fix tests
Do not store expanded action URLs.

They are not portable. STUD-681.

Minor updates.
pylint/pep8 cleanup.
Merge pull request #905 from rocha/datadog-statsd

Remove dogstatsd-python in favor of dogapi
Add a checklist example to test course for import/export roundtrip.
Merge pull request #864 from edx/adam/welcome-email

Adam/welcome email
Fixes extra 'file' that was leftover locally after import
Merge pull request #932 from edx/jkarni/fix/remove-leftover-file

Fixes extra 'file' that was leftover locally after import
Merge pull request #901 from edx/christina/dont_import_checklists

Do not store expanded action URLs.
Merge pull request #559 from hikari-boulders/patch-2

Update discussion.md