Comment moderation actions

This includes: hiding/unhiding, archiving/unarchiving, and unflagging.
Actions can happen on individual rows, or on multiple rows at once
To me this would be easier to read with just one Bacon `map`:
```javascript
batchActionIdStream = batchActionStream
    .map(function() {
            var $elems = $container
                    .find('[data-comment-id]')
                    .has('[data-batch-action-checkbox]:checked')
            return _.map($elems, function(elem) {
                return $(elem).attr('data-comment-id');
            });
    }),
```
Decoding Bacon "function construction rules" always takes some extra brainpower, so when plain old JS doesn't add complexity I think we should favor it.

You could also consider moving this to a function called `getSelectedCommentIds`.

And a question -- does `_.map($elems)` really loop over all items in the JQuery object?? I don't see that in the docs anywhere.