Added JsonModel classes
Added methods for downloading and unzipping file. Added imageName field to the sqlite to save image name of contact.
Added UpdateDetails.plist, changed image names to GUIDs, added isDeleted field to json and db, added ‘version’ field to json.
Used NSURLConnection to download the zip file, refactored the code.
Merge branch 'feature/getting_contacts_from_server_file' into develop