Quick editing an attachment does not correctly generate prefixed eIds of container elements

[longhotsummer]

If the attachment has eId att_3, the parsed elements incorrectly have prefix att_1__.

[longhotsummer]

There are two aspects to this:

1. passing the correct id_prefix to /parse (from javascript to the server)
2. slaw using this correctly (it currently ignores it for schedules)

[longhotsummer]

We currently re-write attachment eIds (only the top-level attachment eId though) in javascript, after parsing an attachment. This means that slaw doesn't need the numbering context.

So the alternative is to re-write eids the whole way down the tree in JS after replacing an attachment.