mod_http_xep227: Add support for import via APIs rather than direct store manipulation In particular this transitions PEP nodes and data to be imported via mod_pep's APIs, fixing issues with importing at runtime while PEP data may already be live in RAM. Next obvious candidate for this approach is rosters, so clients get immediate roster pushes and other special handling (such as emitting subscribes to reach the desired subscription state).

This module writes out a traceback to `traceback.txt` in Prosodys data
directory (see `prosodyctl about`) when the signal `SIGUSR1` is
received. This is useful when debugging seemingly frozen instances in
case it is stuck in Lua code.