Bump to v3.1.4, Marketing Changes, and Update Tests Up to WP 6.9

[chrisjtang]

Description

• Added dismissible admin notice explaining free version ads and paid plan options
• Tested up to WP 6.9
• Bump version to v3.1.4

Motivation and Context

Marketing updates and general plugin maintenance

How Has This Been Tested?

Manual testing + automated testing suite

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• All new and existing tests passed.