replace description with children and make it required in RelatedPage

[katydecorah]

This PR:

• replaces description with children so that we can wrap the component around content and allow our testing tools to check for spelling, etc.
• makes children required - the component looks unbalanced without a description and I think the context is important for the user.

fixes #225

QA Checklist

• No errors logged to console.
• Component is accessible at mobile-size viewport.
• Component is accessible at tablet-size viewport.
• Component is accessible at laptop-size viewport.
• Component is accessible at big-monitor-size viewport.

Open the test cases app locally on:

• Chrome, no errors logged to console.
• Firefox, no errors logged to console.
• Safari, no errors logged to console.
• Edge, no errors logged to console.
• IE11, no errors logged to console.
• Mobile Safari, no errors logged to console.
• Android Chrome, no errors logged to console.

[colleenmcginnis]

allow our testing tools to check for spelling

Brill.