Enable TOC "open" by default
Remove TOC hamburger menu, replace with key shortuct

Click menu was obtrusive and cluttered UI. Shortcuts allow presenters
to keep UI shortcuts to key presses in place of clicks.
Merge pull request #265 from github/curriculum-toc-default-on

Enable TOC "open" by default, add shortcut key toggle support
Merge remote-tracking branch 'origin/master' into curriculum-toc-default-on
Merge remote-tracking branch 'origin/master' into curriculum-help-feature
Merge pull request #267 from github/curriculum-toc-default-on

Curriculum toc default on (continued)
Merge remote-tracking branch 'origin/master' into curriculum-help-feature
Combine Help and TOC toggle into single function
Add help for TOC toggle