Clean up dev dependencies

A clean up of some recent activity regarding dependencies:

1. The matchdep filter in Gruntfile.js was set up to avoid [missing dependency warnings](https://github.com/Modernizr/Modernizr/issues/1154#issuecomment-30296449). If dev dependencies are found, they are allowed to conditionally load [here](https://github.com/Modernizr/Modernizr/blob/master/Gruntfile.js#L218-L225).

2. I moved `grunt-contrib-connect` and `grunt-saucelabs` to devDependencies. They are only used for testing purposes, and have a big impact in install time reduction via npm.

3. Since `grunt-contrib-qunit` is a dev dependency, I've moved it out of the default task. It can be run using the existing `grunt test` command.