browser tests should be started manually

Calling `npm test` now runs all `*.mocha` unit tests, leaving browser tests to be launched with `open test/index.html` or the like.
add browser test runner
get stacktraces from all browsers

![moar staktracse](https://github-camo.global.ssl.fastly.net/88444f193d394e1003e4577afcb636e1768263b7/687474703a2f2f692e696d6775722e636f6d2f6a61636f6a2e6a7067)
run browser tests from travis
encrypt SAUCE_ACCESS_KEY against codeparty/saddle
Merge branch 'feature/sauce' into develop
encrypt SAUCE_ACCESS_KEY against wenzowski/saddle