Allow for a foreground image element

Problem/Motivation

Currently this module assumes the specified image will be used as the background, with other elements layered on top, such as the gradient and type. In some cases it may be desirable to have a foreground image element. For example, if this module is being used to generate social media cards for a Drupal camp website, it may be better to use a camp-focused background image, and show the speaker's image / avatar in the foreground.

Proposed resolution

Allow for another image to be optionally specified. If provided, there should be a way to specify an image style.