get Offline Content Manager
fun getOfflineContentManager(sourceConfig: SourceConfig, location: String, id: String, listener: OfflineContentManagerListener, context: Context, resourceIdentifierCallback: ResourceIdentifierCallback? = null): OfflineContentManager
Gets a OfflineContentManager for the given parameters. A root folder needs to be provided in location. Multiple OfflineContentManager can have the same root folder. id has to contain an identifier for this source that is unique within the location and must never change. The root folder will contain a folder based on this id. A ResourceIdentifierCallback can be provided to uniquely identify resources if URLs in a downloaded source change.