Blabber Age Verification CSS Support

[jasperf]

This pull request introduces age verification support to the Banner Container Plugin, enabling banners to be hidden based on user age selection via JavaScript-based modals. It includes updates to the plugin's version, documentation, CSS, and JavaScript requirements to support this functionality.

Age Verification Functionality:

• Changelog Update: Added details about the new age verification feature, including CSS support, compatibility with Ad Inserter, and JavaScript requirements. (CHANGELOG.md, CHANGELOG.mdR5-R13)
• CSS Enhancements: Introduced a .d-none class and specific targeting for Ad Inserter and Blabber footer banners to hide elements when age restrictions apply. (public/css/iwz-banner-container-public.css, public/css/iwz-banner-container-public.cssR6-R16)

Documentation Updates:

• Development Guide: Added a comprehensive guide for implementing the age verification modal, including JavaScript functions, modal HTML structure, and integration requirements. (DEVELOPMENT.md, DEVELOPMENT.mdR167-R253)
• README Update: Documented the age verification feature, including an overview, compatibility details, and setup instructions. (README.md, README.mdR126-R177)

Plugin Version Update:

• Version Bump: Updated the plugin version from 1.9.0 to 1.9.1 to reflect the new feature. (iwz-banner-container-plugin.php, [1] [2]