e2e-tests: Rewrite tests in python instead of javascript

This will make it easier for me to write integration tests in the
future. For example, a test that does a `git push` to the test-pack git
repo on the backend, and verifies that the list of tests is updated in
the Web UI.

This uses python-selenium[1]. The main functionality we'll miss from
protractor are Angular-specific locators, like `by.binding`; we'll have
to make do with CSS selectors instead.

[1] http://selenium-python.readthedocs.org/en/latest/index.html
Travis CI: Run `make check` (jshint static analysis)

I don't intend to run the end-to-end tests on Travis, because those
tests require an stb-tester-service backend, which in turn requires
docker, which isn't available on Travis. Also because in the future the
end-to-end tests will probably require a real "stb-tester ONE"
appliance.

Note that Travis already runs `npm install` automatically.

Note that the previous contents of the `.travis.yml` file came from
the angular-seed template, but we never actually used it (we hadn't
enabled Travis for this git repo until now).