Professionalization of the NestedSortable plugin

I would like to help with the future development of the NestedSortable plugin. This pull request introduces Grunt for task automation, together with JSHint validation.

This is a good step to get to a more professional level with the plugin. We can start building on the Gruntfile I have introduced, to automate as much as possible.

My next step would be to:
* reorganize the source folder structure
* fix the demo-files so they use the Bower components and our own source-files
* introduce a task to generate a distribution of the plugin

I'm very curious what you think of this. Looking forward to your feedback!