Embed Privacy missing escaping for show_all attribute in opt-out shortcode

The `Embed Privacy` plugin for WordPress that prevents the loading of embedded external content is vulnerable to Stored Cross-Site Scripting via `embed_privacy_opt_out` shortcode in versions up to, and including, 1.8.0 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers with contributor-level and above permissions to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. Version 1.8.1 contains a patch for this issue.