TravisCI Integration

This pull request integrates privly-chrome with TravisCI. This required some interesting approaches to loading the Chrome extension onto SauceLabs.

* The Chrome extension is loaded as a signed and packaged extension, which is then base64 encoded and streamed to SauceLabs.
* The content server for the selenium tests runs from TravisCI over SauceConnect, so SauceLabs can still connect to a localhost:3000 server.
* The private key used to package the chrome extension on TravisCI is public knowledge and should not be used for any other purposes.