Move unit test plugins to devDependencies

To avoid unnecessary downloads and compilation, I've moved the unit test Grunt plugins into devDependencies. I'm also taking a page from Yeoman and using [matchdep](https://github.com/tkellen/node-matchdep) to dynamically load npm modules. This vastly reduces Modernizr install time via npm.

For devDependencies, I now check to make sure the dependencies are installed before requiring them to avoid import errors. This method allows me to require Modernizr and not have to include unit tests in the dependencies array.

I also took the opportunity to add metadata to the Modernizr API.

This should be the final PR needed to address #695