https://issues.liferay.com/browse/LRDOCS-1286

https://issues.liferay.com/browse/LRDOCS-1286

For simplicity's sake, removed support for multiple types of sidebars. Also simplified the Markdown syntax for sidebars. Now, use '+\$\$\$' to begin a sidebar and '\$\$\$' to end a sidebar. Blank lines must appear above and below the tokens so PegDown parses the tokens as paragraphs.

@sez11a