Build: Adds browserstack.json

Configuration for https://github.com/browserstack/browserstack-runner
Requires BROWSERSTACK_USERNAME and BROWSERSTACK_KEY env vars to be set.
Will look into Travis integration later.

Closes #601
Core: Removed obsolte JSHint setting, was for a Grunt 0.3.x workaround

Closes #602
Build: Update license

Closes gh-580