Roy/Sid |13|Added API(s) to retrieve course,module,chapter and message

Added version field to all Content DTOs
Separated Interfaces for Course,Modle,Chapter,Node
Megha/Sid/Sharvani |14| Added API to retrieve and add bookmarks. MTraining can now take version from platform.

Change-Id: Icdefa73f77c4ae4c5f18b66f8ce6d5a5bd8b3719