Update shrinkwrap

No changes.
Add JS test harness

Changes:
* Add initial JS tests and tests bundle task (say that 10 times fast) to
  gulp build file
* Add the testem HTML harness during provisioning (development only)
* Add ./scripts/testem.sh to run JS unit tests in a browser window
* Add testem (ci mode) to ./scripts/test.sh to run tests on Jenkins
Fix lint
Add Xvfb support for JavaScript tests

This changeset installs the X virtual framebuffer (Xvfb) so that Testem
can drive a headless Firefox.
Add watchify-tests command

We observed very strange behavior mixing watchify with gulp.watch... The
simplest solution seems to create a separate task just for watching
tests.

It's important to lint JS before running browserify in order to prevent
the watch command from exiting with an error status.