Add scope/field selector settings for LinkedIn provider.

This change adds three new configuration variables to third_party_auth's LinkedIn provider:

* SOCIAL_AUTH_LINKEDIN_OAUTH2_SCOPE,
* SOCIAL_AUTH_LINKEDIN_OAUTH2_FIELD_SELECTORS,
* SOCIAL_AUTH_LINKEDIN_OAUTH2_EXTRA_DATA

Being able to configure these additional settings is useful if you want
the LinkedIn provider to pre-populate the email field when a new user
registers via the linkedin provider.

The Google provider prepoulates the email field by default, but if you
want LinkedIn to do the same, these two settings should be set to:

SOCIAL_AUTH_LINKEDIN_OAUTH2_SCOPE = ['r_basicprofile', 'r_emailaddress']
SOCIAL_AUTH_LINKEDIN_OAUTH2_FIELD_SELECTORS = ['email-address']

For more info see:
http://psa.matiasaguirre.net/docs/backends/linkedin.html
Add redirect.
Add url redirect to.
Update error code.
Fix unit test.
Move js import into courseware js group.
Use confirm dialogue.
Explicitly skip tests in common unless we know we're running the LMS unittest suite
Prevents students from accidentally changing their enrollment on login (LMS-2773)

skip tests if not run in lms
Fix unit test.
Initial draft moving key creation out of wiki
Add test that xml body was parsed successfully.
updating diff-cover to 0.5.0
Review draft, one more flowchart to come
Merge pull request #4219 from edx/clytwynec/diff-cover-update

updating diff-cover to 0.5.0
Increases wait_for_notification timeout to 60 seconds
Uses present in bokchoy test
Additional flowchart
Merge pull request #4223 from edx/benmcmorran/increase-notification-timeout

Increases wait_for_notification timeout to 60 seconds
some of Sylvia's edits