LRDOCS-1023 Added seven article files for the Service Builder learning path. Converted the what-is-service-builder section to a learning path article. Started converting the object-relational mapping section to article format. Replaced nosester with liferay.docs in package and path names in the article
Merge branch 'master' into LRDOCS-1023
LRDOCS-1023 Refactoring defining-an-object-relational-mapping article so that article presents generic steps (i.e., doesn't assume that the reader will follow along with the Event Listing portlet project
LRDOCS-1039 Converted Dev Guide's portlet model hints section of Service Builder chapter to tutorial article
Merge pull request #884 from jrao/LRDOCS-1039

https://issues.liferay.com/browse/LRDOCS-1039