Add jshintrc

From https://github.com/crowdtap/javascript/blob/master/linters/jshintrc

Modifications from Airbnb's jshint options:
* Adds `mocha` environment
* Adds predefined globals from assets.shared
* Adds `freeze` option (prohibit modifications to native objects, i.e. `Array`, `Date`, etc.)
* Removes single quotes for strings requirement