LPS-33007 Obtain palette items for the Application Display Templates

from @jorgeFerrer 
The classPK parameter of getTemplateVariablesMap() is not used yet in the implementations included in this pull, but it will be used in upcoming implementations.

We will include javadocs once this is reviewed.

I have hardcoded the Javadoc URL in a JSP. I wasn't sure if a portal.properties property was better. Let me know if you think so.