Plugin should add `utilities` instead of `components`

[f15u]

Working on #14, I noticed that classes are added components instead of utilities.

As stated in the official tailwind docs, components should be used for, citing, "[...] opinionated, complex classes like buttons, form controls, alerts, etc [...]".

I think we should reflect that.

This is a breaking change because people could not be using @tailwind utilities layer in their css and the build would fail. On the other hand not using @tailwind components the plugin is not going to work as expected like in our project.