enhancement: re-format main file

[mathetos]

The code structure of the plugin needs to be updated to the standards of our newer free add-ons. Better organization, more consistent use of GiveWP classes and structure.

Here's a quick list:

• Update the main file to the same structure as our free addons class
• Ensure we're using modern language support
• Ensure we're implementing a delayed admin notice correctly
• Ensure we're checking for minimum GiveWP version correctly
• Ensure we're extending the form meta settings correctly