Pin coffee-script version to 1.6.1.
Add test for at least one group before saving a group configuration
Merge pull request #4973 from edx/tim/single-group-is-ok

Update test_group_configuration_validation on single group allowed
Merge pull request #4969 from edx/benp/fix-js-tests

Pin coffee-script version to 1.6.1.

1.6.3 is causing some issues.
Replace reference to Google OpenSans with edX-hosted OpenSans
Addressed comments.
Fixed path to font files.
Use Bourbon mixin utility instead.
Ordered font declarations by increasing font-weight
Fixed wrong path to one font file.
Removed reference to fonts.gstatic.com that was left in non SASS-generated CSS file.