Begin running routes to controllers through channels.

This is still a work in progress, but ultimately a controller function
will take an input channel and return an output channel. On each route
invocation, we can put the route params into the input channel of the
desired controller, and a template-context pair will appear in its
output channel. From there, we can just execute the template, providing
the context as an argument. Nice and easy.

Templates don't do any async work, but controllers can; so controllers
are channel based while templates are not.
Allow :prevent-default symbol in ui/listen args.

Since preventing the default click behavior is a common desired side
effect when generating a ui/listen channel, it is now possible to supply
a symbol which has that effect. The alternative was to write a zillion
one-off #(.preventDefault %) functions, which, although not exactly
onerous, was not necessary either.
Rename videoList.html to video_list.html. New convention.
Basic templating proof of concept.
Use Enfocus clone-for to display video list.
Allow application/edn media type.

This will make life easier when loading from the API into the
ClojureScript webapp, while preserving JSON output for clients that want
it. Unfortunately, there are still some glitches with the EDN
round-trip; see issue #2.
Let data/GET take an optional media-type param.

I wasn't able to fully read the EDN back into ClojureScript, but this
sets up the ability for later.
Final templating step: use templates and snippets.