LMS: resolves missing certificate download button styling
* adds in Sass placeholder to mirror older/inherited button styling used in LMS
* uses light theming Sass variables for button styling
* adds specific selector for certificate download button
small bugfixes for theming+sass+templates

change ruby and to &&
Studio/LMS: Updates copyright notices to 2014
Merge pull request #2164 from edx/talbs/update-copyright

Copyright Notice Updates
Add individual due dates feature.

Adds a feature to the edX platform which allows instructors to set
individual due dates for students on particular coursework. This code is
meant primarily for on-campus use--it is not intended that this feature
would be used for MOOCs. It adds a new tab, "Extensions", to the beta
instructor dashboard which allows changing due dates per student. This
feature is enabled by setting FEATURES['INDIVIDUAL_DUE_DATES'] = True.
Merge pull request #2062 from jazkarta/feature-idde2

Individual Due Date Extension feature
Merge pull request #2163 from edx/jbau/sass-path-bugfix

small bugfixes for theming+sass+templates
Merge pull request #2159 from edx/talbs/lms-fix-certificate-button

LMS: FIX - Add Styling Back to Certificate Download Button
Clean up some pre-existing formatting.
Remove unused things.
Rename DbModel to KvsFieldData.
Implement InheritanceFieldData
Use XBlock xml serialization and deserialization

XModules continue to use their own interface for xml, but provide an
adaptor that makes the the XBlock interface available.

[LMS-179]
Prevent unicode data from being injected into a Location using the _replace function