main: incorporate some private-only UI stuff from supermodule.
main: more UI logic.
main: auto-rotate to nav item based on document.location.hash.
Factor mockterm into a submodule (https://github.com/Ubehebe/term.js).
Merge branch 'master' into private
Merge branch 'master' into private

Conflicts:
	Makefile
(private branch only) Add Google Analytics event for tutorial completion.
Resolve merge conflicts with prior remote private branch.
Merge branch 'private' of ~/Dropbox/r5js/r5js