Preserve images within figure elements

This CL fixes an issue where images nested within `<div>` elements inside a `<figure>` tag were being incorrectly removed by Readability's cleaning process. Specifically, a structure like `<figure><div><div><img></div></div></figure>` would first be transformed to `<figure><div><p><img></p></div></figure>`, and then the outer `<div>` (and its contents) would be erroneously identified as extraneous and removed. The fix introduces a targeted exception within _cleanConditionally(). It prevents the removal of `<div>` elements that meet the following criteria: * The element is a `<div>`. * The `<div>` is an ancestor of a `<figure>` element. * The `<div>` contains a single `<img>` element (potentially nested). Also add test case allrecipes-1 taken from: https://www.allrecipes.com/hot-honey-brussels-sprouts-recipe-11832010