'Return a dictionary containing the actions and associated roles on item
where item is one of Library, LibraryFolder, LibraryDatasetDatasetAssociation,
LibraryDataset, Dataset.  The dictionary looks like: { Action : [ Role, Role ] }.'

def get_permissions(self, item):

    permissions = {}
    for item_permission in item.actions:
        action = self.get_action(item_permission.action)
        if (action in permissions):
            permissions[action].append(item_permission.role)
        else:
            permissions[action] = [item_permission.role]
    return permissions
