'Upload book cover to the device. Default implementation does nothing.
:param path: The full path to the directory where the associated book is located.
:param filename: The name of the book file without the extension.
:param metadata: metadata belonging to the book. Use metadata.thumbnail
for cover
:param filepath: The full path to the e-book file'

def upload_cover(self, path, filename, metadata, filepath):

    pass
