Use ejs templates in browse JS

[jfirebaugh]

There are a few other JS-related cleanups in this PR, but
the main commit replaces the tedious manual DOM manipulation
with EJS templates.

EJS is sort of the lowest common denominator JS templating
language. It would be fairly easy to port to mustache or
something if anyone has a strong preference. I've purposefully
kept the templates pretty much logic-free.

[tomhughes]

I'm all for something along these lines, so I'd love to hear what other people think both in general and about what JS templating system we should use.

[tomhughes]

Nobody objected to this, so I merged it, mostly because I wanted it for my work on the notes code ;-)