Update success/error messages to WP admin notices

[jeffpaul]

Is your enhancement related to a problem? Please describe.

When saving the plugin settings page / updating the selected list, there are various success/failure messages that get shown at the top of the page. Instead of using custom UI for that, let's utilize the WP admin notice format as a more familiar UI for WP users.

Designs

Sample UI that would ideally be changed to standard WP admin notices:

Describe alternatives you've considered

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

[MaxwellGarceau]

Making notices and comments inside Teamwork task.