add Viewer To File Descriptors
abstract fun addViewerToFileDescriptors(fileDescriptors: List<RainbowFileDescriptor>, viewer: RainbowFileViewer, listener: RainbowListener<List<RainbowFileDescriptor>, Map<Int, List<RainbowFileDescriptor>>>? = null)
Adds a RainbowFileViewer to as list of RainbowFileDescriptor