'Saves the asset metadata for a particular course\'s asset.
Arguments:
asset_metadata (AssetMetadata): data about the course asset data
user_id (int): user ID saving the asset metadata
import_only (bool): True if importing without editing, False if editing
Returns:
True if metadata save was successful, else False'

@contract(asset_metadata='AssetMetadata')
def save_asset_metadata(self, asset_metadata, user_id, import_only):

    raise NotImplementedError()
