Javadoc for search/searchCount methods

Hi Eudaldo,

For Javadoc Thursday, I'm in the process of adding Javadoc to the *JournalArticleLocalServiceImpl* class to document new methods.

I've added several new method descriptions for methods that you introduced (from this [commit](https://github.com/liferay/liferay-portal/commit/f43bf6ecf79a7a243c9c6d57c055250a232532d3)), and request you to review them to make sure they're accurate. I've modeled the Javadoc to stay consistent with other Javadoc in the class.

Please let me know if anything in particular should be added to the search/searchCount methods' Javadoc that would be important or distinguishes it from the other search methods, or if there are any inaccuracies. Feel free to edit the Javadoc directly and send a PR back to me, if it's more convenient. I've added five method descriptions in total.

Thanks!