Add pagination attribute allowing always shown prev and next buttons

[angelasheppard]

Adds a boolean attribute to the pagination component allowing the previous & next buttons to always be shown on the boundary pages. Defaults to current behavior (prev not shown on page 1, next not shown on last page).

Buttons shown on those boundary pages are disabled and reduced opacity.

Loom of the live boilerplate page

Resolves #140

[nhobes]

This is great, thanks so much for contributing! 🙌