LPS-50448 - Migrate Message Boards portlet aui-base javascript

Hi Rob,

Attached is an update for https://issues.liferay.com/browse/LPS-50448.

I implemented the form plugin inside the script tags that I had already made changes to.  I also removed the selectCategory method from edit_message.jsp, as it doesen't seem to ever be used since 5114300 was merged in.

Please let me know if there are any issues.

Thanks!