Decouple from Grunt

[addyosmani]

We're at the point where a number of our most popular generators do not use Grunt. With this in mind, I think we should consider dropping or refactoring the messaging on our homepage to make it clear yo can be used to scaffold out a setup with any tooling choices.

Depending on how far we wanted to take it we could illustrate this point with examples.

E.g: Yo works great with Grunt. Check out generator-webapp. Yo also works great with Gulp. Checkout generator-gulp-webapp. It even works well with X, Y and Z which have nothing to do with either of these options.

If we decide to do this properly, we would also need to refactor the learning section of the site. Thoughts?