Allow role visibility settings

Problem/Motivation

Role visibility can't be set on this checkout pane.

This becomes a problem is if, for example, you have the custom checkout message on the first step of the form which normally gets skipped when people are logged in. Then they see the message and cannot proceed forward through the checkout process.

Proposed resolution

Add role checkboxes to the pane config.

Remaining tasks

Test patch and review.

User interface changes

Additional role checkboxes on pane config.