Added grunt colorguard task

Adds [CSS Colorguard](https://github.com/SlexAxton/css-colorguard) as a grunt task during dev build

### Changes

* Added [grunt-colorguard](https://github.com/elliottwilliams/grunt-colorguard) to `packages.json`
* Added `colorguard` to `build:dev` task in `Gruntfile` template

### Review

@germanny 
@ericrasch 
@jameswlane 

### Notes

CSS Colorguard is awesome for catching colors that are indistinguishable by the average user. Awesome for reducing unnecessary stylesheet overhead.