Standardize formatting

This PR alters the code to be more consistent with WP core JavaScript and the WordPress Core [JS coding standards](http://make.wordpress.org/core/handbook/coding-standards/javascript/). Specific changes

* Standardize on single-quotes
* Clean up gruntfile syntax (remove leading spaces before colons)
* Add WP core's .jshintrc file
* Added JSHint task to Grunt, and fixed the errors it called out
* Standardize whitespace in function declarations and arguments (I may have missed some spots here)
* Switched spaces to tabs, to match WP core