Update opaque-keys library to use block_id for html_id for new keys.
Catch more places where get_children was giving us version aware references.
LMS-11237
Merge pull request #4960 from edx/split/html_id

Update opaque-keys library to use block_id for html_id for new keys.
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.