Lrdocs 1489 friendly url learning path

Created intro article and two learning poath articles.
00-intro introdues the concept of Friendly URLs.
01-creating-url-routes goes through the additions to liferay-portlet.xml and creating URL routes in the -friendly-url-routes.xml file.
02-removing-the-primary-key-from-portlet-urls goes through getting rid of the Primary Key from URLs. It includes:
    -Creation of a new Action method in the controller
    -Alterations to the current controller methods thst rely on the Primary Key being in the request
    -Modifying the service layer by adding finders to service.xml and using them to create getter mehod is the local service implementation classes
    -Modifying the JSPs, especiually URLs and scriptlets, to remove Primary Key parameters from the URLs

Changes to the code in the learning-sdk reflect the code snippets included in the Articles.
https://issues.liferay.com/browse/LRDOCS-1489