Adding multiple widgets to an entity browser results in validation error

Problem/Motivation

When adding a Pixabay widget to the entity browser, the allowed extensions field is populated via AJAX, when selecting a media type. When adding multiple widgets, the AJAX wrappers aren't unique, this results in a validation error.

Steps to reproduce

• Follow the installation/configuration steps in the readme file of the module
• After adding the widget to the entity browser,save the form and add another widget of the same type (Pixabay)
• Select a media type in the widget -> Allowed extensions field of the first widget gets updated
• Try to save the widgets -> Validation error

Proposed resolution

Add unique wrapper IDs/name attributes "Allowed extension" form element.