editor: load javascript later (if we can)
editor: load javascript later (if we can)

We don't need viz.js until the very end, and it's a heavy-weight
resource, so move it later.

Signed-off-by: Daniel Halperin <1a02732a15f637c31107256cbee5819e36aa7c67@cs.washington.edu>

uwescience/myria-web,uwescience/myria-web,uwescience/myria-web,uwescience/myria-web