Comments in NodeDataProvider about refactoring  getPathToJSONFile
Added functionality to get existing content from a zip file. Refactoring of ContentManager.
Moved zip file of content.
Added lazy instantiation of nodeObjects in NodesTableViewController.
Changed define used with observer to extern.
Cocoapods update.
Refactoring of getPathToJSONFile method from NodeDataProvider.
Refactoring of downloadZipFromURL in ContentManager
Refactoring of file paths
Refactoring of file paths, using Objective-C naming conventions for getters.
Added initial version for existing content
Fixed download issue due to appending of zip string in ContentManager. Changed const name in ContentManager.
Added TODO comments