Footer Start Banner Enhancement

[jasperf]

This pull request introduces enhancements and updates to the iwz-banner-container-plugin, focusing on adding support for multiple banners and device targeting in the "Blabber Footer Start" location, along with version updates and code improvements. Below are the most important changes:

Feature Enhancements:

• Added support for multiple banners in the "Blabber Footer Start" location, allowing users to add and manage multiple banners. [1] [2]
• Introduced device targeting for banners in the "Blabber Footer Start" location, enabling banners to target desktop, mobile, or all devices.

Admin Interface Improvements:

• Updated the admin interface for "Blabber Footer Start" to include an "Add Another Banner" functionality and align with other multiple banner locations.

Version Updates:

• Updated the plugin version from 1.8.0 to 1.8.1 in iwz-banner-container-plugin.php and defined constants for consistency. [1] [2]