New component: Modal Dialog

[gjones]

Summary

We need a modal dialog component for rendering content above the main window.

Recommended props

dismissOnClickOutside: boolean (if False, also hides the `x` icon button)
title: string
description: string (if empty then display:none)
children: ReactNode
button1: Button (primary)
button2: Button (secondary)
button3: Button (secondary)

Provided tokens