Adds basic block

[nateconley]

Description of the Change

Follows behavior of legacy widget.

• When focused, display message with link to settings page.
• When not focused, preview the block

Adds some basic support items like color and spacing

Partially Closes #2

How to test the Change

1. Add block to a post or page.
2. Block displays on front end

Note if testing with Twenty Twenty-One: not all frontend styles (especially for forms) are reflected in the block editor.

Changelog Entry

Added - New block

Credits

@nateconley

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.