Update date range advisory text to display no matter what range is selected

[wwhorton]

Removes conditional and variables so that text is displayed all the time; adds top margin class to give some space between the text and the date range buttons.

Changes

• Removes conditional from DateFilter.js and adds u-mt15 class

Testing

• yarn test should pass
• Visit CCDB and click date range buttons; text should always be visible

Screenshots

Checklist

• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows the standards laid out in the front end playbook
• Passes all existing automated tests
• New functions include new tests
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged
• Visually tested in supported browsers and devices
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)

[contolini]

@wwhorton Code looks good and works as expected 🎉 Locally, I'm seeing a test failure I think because this snapshot line needs the new className="u-mt15" added to it.

[contolini]

Merging this so I can cut a release and deploy to demo.