ant check-headers

Hi Rich,

Mike added a target named check-headers that makes sure our markdown files start with h1 headers. It's a dependency for the dist target and fails the build if a markdown file does not start with an h1 header. It works well. I just did a quick clean of the XML and Java code.

Note, I merged in the fixed JAR commit from https://github.com/sez11a/liferay-docs/pull/1012.

https://issues.liferay.com/browse/LRDOCS-1352