LRDOCS-1031 Converted Liferay Plugins SDK section of Dev Guide into a tutorial, updated content
LRDOCS-1031 Added required image for Plugins SDK tutorial
LRDOCS-1031 Updated references to Dev Guide sections to references to Dev Site tutorials
LRDOCS-1031 Fixed typo
Merge pull request #901 from jrao/LRDOCS-1031

Created tutorial on using the Liferay Plugins SDK