Save "Preview theme" state; resolves #13940
fixes #13968
Merge pull request #13954 from hnrch02/persist-preview-theme

Save "Preview theme" state; resolves #13940
Update to Jekyll 2.1.x.
fix #13979
Fix inconsistency between demo and displayed code for modal demo

Fixes #13991
Merge pull request #13992 from pjrobertson/master

Fix inconsistency between demo and displayed code for modal demo
Update dependencies.