Wiki image syntax is not supported by GitHub-Flavored Markdown 1.0

Steps to reproduce:

1. Create a page in the markdown+github/1.0 syntax with the content ![[Logo|Sandbox.WebHome@XWikiLogo.png]]
2. View the page

Expected: the XWikiLogo.png image attached to Sandbox.WebHome is displayed, as it is on a markdown/1.2 page.
Actual: a "!" followed by a link to create the page Sandbox.WebHome@XWikiLogo.png is displayed.

Cause: the wiki image syntax is enabled with WikiLinkExtension.IMAGE_LINKS in DefaultMarkdownConfiguration only. MarkdownGitHubConfiguration doesn't set it.