Easy Digital Downloads - Custom prices 1.5.7

Fix: Deprecation notice in PHP 8.
Fix: Improve user input sanitization.
Fix: Update header to use Plugin URI.

Fix: "Undefined variable: button_text" when displaying custom price input on the front-end.
Fix: Bonus item could be added to cart twice under some circumstances.
Tweak: Remove set width from custom price input field.
Tweak: Update plugin author to "Sandhills Development, LLC".
Tweak: Increase the width of admin "Min" input field for improved readability.

New: Added translation files
Fix: Translation files not loaded