Include the field_id in the context of _as_table_helper
This makes it possible to refer to the field that is being edited by
it's ID (in for example Javascript).
Patch by: "Mario Ferraro" <fadinlight@gmail.com>
Benjamin Niemann <pink at odahoda dot de>: Main developer of Python target.
Clinton Roy <clinton.roy at gmail dot com>: AST templates and runtime.