Added support for browser testing

Browser tests are written using selenium and can be run locally or remotely using the SauceLabs service (see a test session here: https://saucelabs.com/tests/1971fbecd84149168269abb944a78b27)

The tests are run with a different test runner so running ./manage.py test does not run the browser tests, see docs/devel/source/browsertests.rst for more details

It also integrates with travis, for the travis integration you will need to add a couple of environment variables (under the repository settings > environment variables):

SAUCE_ACCESS_KEY
SAUCE_USERNAME

Please contact me in a private email for these values.