* Return sensible HTTP status for ActivityPub inbox processing
* Return sensible HTTP status for salmon slap processing
* Return additional information to debug signature verification failures
* Move ApiController to Api/BaseController
* API controllers inherit from Api::BaseController
* Add coverage for various error cases in api/base controller
Fix#2196 - Respond with 201 when Salmon accepted, 400 when unverified
Fix#2629 - Correctly handle confirm_domain? for local accounts
Unify rules for extracting author acct from XML, prefer <email>, fall back
to <name> + <uri> (see also #2017, #2172)
