Make the messages dismissable for a limited period

[moorscode]

We need to make the messages triggered by WHIP dismissible.
The dismissal should not be forever, but site-specific.

Implementation details:

• dismissal should be done on a specific version check
• the message should be dismissed for a month

This would allow for PHP version requirement bumps, which trigger the new message directly.
Also makes the message sticky enough to return without having the dependency on a specific plugin or plugin version.

Original issue: Yoast/wordpress-seo#7477