feat(pagination): allow for prev/next and first/last graphic customisation

[mlarcher]

In v0.5 there is no way to tell if a link in the pagination is a page number or a next/previous or first/last link (except by testing page.text, which is kind of ugly for the purpose).
That would be useful in order to style them differently.

[bekos]

This project is very specific about styling support and we already support the default bootstrap classes for pagination.
Also, your case does not seem so common since neither bootstrap distinguishes elements in the pagination list.

As you said, you can override the default template and test the page.text, page.number and/or the current $index to decide your actions. I agree that it is not that elegant, but I don't think we are going to handle this situation inside the library.