nmbug.js: Use bind to avoid forwarding message_id through _get_tags

nmbug.js: Use bind to avoid forwarding message_id through _get_tags

Instead of telling _get_tags that the callback will always want the
message_id (in addition to the list of that message's tags), use bind
[1] to add that information when we set the _edit_tags callback.

[1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind