If `delete_device_after` is configured, that period should be counted for webxdc instances from the
last status update, otherwise nothing prevents from deleting them. Use `msgs.timestamp_rcvd` to
store the last status update timestamp, it anyway isn't used for anything except displaying a
detailed message info. Also, as `ephemeral::select_expired_messages()` now also checks
`timestamp_rcvd`, we have an improvement that a message is guaranteed not to be deleted for the
`delete_device_after` period since its receipt. Before only the sort timestamp was checked which is
derived from the "sent" timestamp.
Move DebugLogging into debug logging module.
Remove Context.send_log_event().
Use blocking_read() instead of try_read() to
get read lock on debug_logging() in synchronous code.
Do not try to log events while holding a lock
on DebugLogging.
