remove vestigal signald-derrived data model quirks
context
- in building signalc, we chose to adppt without modification some questionable data model choices from signald in order to avoid breaking the contract with signalboost (and thus achieve a smooth cutover)
- in some cases, we changed the data model and added shims in signalboost to handle both formats (the old signald format we didn't like and the new signalc one we prefer)
- once signalc is shipped, we would like to go back and remove all vestigal signald-imposed data structures that we don't like
- the purpose of this MR is to collect them all in one place and fix them in one go (if scope allows)
items to change
- unnecessary grouping of a signle
SendResult
into a one-element list of SendResults
- unnecessary/inconsistent
data
nesting in all responses
- inconsistent formatting of sender/recipient (esp. in identity failure error messages)
- inconsistent formatting of inbound/outbound attachments
- inconsistent error handling btw send results (network error, identity failure, etc) and decryption errors(?)