Sauce Integration 

Can someone review this, I haven't worked with `karma` before. Tests pass locally, but the sauce component is still untested.

Based the `karma.conf-sauce` file on [angularjs's karma sauce integration](https://github.com/angular/angular.js/blob/master/karma-shared.conf.js)

(BTW Sauce accounts are Jeremy's)
I can from https://github.com/megawac/underscore/commit/3f341d426b9b3257a58b4d66a7a1c63c2b932103.

It's nice to see projects [aligning on testing](https://github.com/lodash/lodash/blob/d7f568dccc354331385eb86bf9f8e427f77e53ff/test/saucelabs.js#L98-L119).