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
Added Brandon DeRosier to authors
Datetime localized on gitlog page of sysadmin dashboard
ModulestoreEnum class.
Adds is_xblock_visible_to_students
Fix branch settings.
consolidate new post form variants into single client-side template/view
Fixed IE security warning on course page.
LMS-2892
Merge pull request #4232 from edx/nimisha/modulestore-enum-constants

ModulestoreEnum class.
ORA2 release-2014-06-30T13.39; update EASE to bump the NLTK version to 2.0.4
Merge pull request #4215 from edx/waheed/lms2892-ie-security-warning-fixed

Fixed IE security warning on course page.
Merge pull request #4252 from edx/will/ora2-release-2014-06-30T13.39

ORA2 release-2014-06-30T13.39
Merge pull request #4229 from edx/studio/uses-mixed-modulestore-xblock-visibility

Adds is_xblock_visible_to_students
Merge pull request #4050 from mtyaka/linkedin-email

Make LinkedIn auth provider request email by default.
Merge pull request #4210 from bdero/bdero/fix-sysadmin-dashboard-gitlog-timezone

Make sysadmin dashboard gitlog date timezone-aware
Merge pull request #4216 from edx/jsa/new-post-redesign

consolidate new post form variants into single client-side template/view
Get active student count from new analytics data API

Disabled by default.
Uses ModuleStoreEnum in is_xblock_visible_to_students
Merge pull request #4234 from rocha/rocha/analytics-active-count

Get active student count from new analytics data API
Merge pull request #4259 from edx/benmcmorran/fix-xblock-visibility

Uses ModuleStoreEnum in is_xblock_visible_to_students