CI move to BrowserStack

Tests were broken due to a peerDependencies conflict, a karma plugin required karma@0.12

This PR provides 3 things:
- upgrade to karma@0.12
- test command simplification (local vs. BrowserStack availability)
- extensive browser coverage (17 different configurations)

BrowserStack account is paid and provided by the BBC.
SauceLabs has been decommissioned.

![](http://i.imgur.com/c0Vhh0i.gif)