Configure/Setup Travis CI and Sauce Labs

[DrewML]

• Setup Travis CI config, along with Sauce Labs/Sauce Connect
• Updated testing info in CONTRIBUTING.md
• Build will always run before executing tests
• Moved e2e tests into grouped folders
• Added gulp task (newtest), that can quickly scaffold the basic structure for an e2e test
• Scenario server now uses angular lib paths in angular-versions.conf.js, rather than following a separate convention
• Updated the scenarios listing/index at / on the scenario server, to use express templating. Now lists all available Angular versions
• Enabled tests for Firefox
• Added browserify to package.json, because I apparently had missed it before, which means gulp builds would have failed for anyone who didn't have browserify installed globally. Whoops!

[DrewML]

When this PR is merged, CI should automagically start working at https://travis-ci.org/rev087/ng-inspector. (Example passing on my fork: https://travis-ci.org/DrewML/ng-inspector/builds/75030943)

The message about Travis using the "legacy infrastructure" should also go away.

Finally, you should then be able to add a Travis CI badge in the README.md for the repo.

[![Build Status](https://travis-ci.org/rev087/ng-inspector.svg?branch=master)](https://travis-ci.org/rev087/ng-inspector)