Merge pull request #76 from oerpub/58657378-boxes-and-spacing

remove italics-related styling for quotations
Merge pull request #77 from oerpub/semantics-drag-below-fold-57739880

let semantic blocks scroll with content (github-bookeditor half)
improve header styling

Remove the borders, use better sizes, don't let letter-spacing inherit
past h1, use same margins as paragraphs.

Forthcoming (though I think relatively nondependent) commit coming on
Aloha-Editor
Merge branch 'refs/heads/improve-header-styling-58912428' into testing
Merge branch 'testing' of github.com:oerpub/github-bookeditor into testing