Selenium Testing

This pull request adds selenium testing to privly-firefox by calling the selenium tests defined in the privly-applications module. The tests are run on SauceLabs in the extension context.

Note: the TravisCI script downloads and loads the privly-web server so it can act as a content server for the extension running on SauceLabs. Please take a moment to think about how cool it is that pushing a commit to GitHub triggers a continuous integration service to download/run a webserver and push a JS application to a browser virtualization service that runs application code defined in a browser extension.
Should this be kept to `github.com/privly/privly-web`?