Add d3.js to project

Using d3 to create a geographic view of trains will aid in debugging
Add Grunt and .jshintrc, then fix JSHint errors

This Gruntfile is based on the one in the Yeoman sample app
(Most of its functionality was commented out with wild abandon)
`grunt watch` task is configured to catch JSHint errors
Add additional Red Line sample data
Add d3 state rendering

* Switch to lodash.underscore.js to regain access to `_.chain()`
* Add d3 and topojson globals to .jshint
* Overload TrainsView to push data to d3-rendered SVG element
Add geographic plot of train locations using d3.js
Refactor Line model to support alternate subway lines

* Adds Orange line sample data
* `url` option must be passed in to constructor on Line creation
* Each line renders in its own div -- that can probably be cleaned up