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
This `watch` can't be right.  `browserify-tests` doesn't copy files to the `versionedDir` or run `collectstatic`, so the new bundle will never make it's way to `testem`.

In addition, you should be watching *all* JS files (or at least both `test` and `src`), because they are *all* included in the bundle.  For a TDD test/debug cycle, if you write your unit tests upfront, you'll want the tests to be rerun whenever you change a source file.