Shorten the daemon log lines

Each log line names the event in a few plain words, then the cause after
a colon, such as "telegram: receive failed: 502 Bad Gateway (retry in
2s)" or "whatsapp: connected again after 1m25s". The lines no longer
explain what the event means for the user: they stay short enough to
read in the journal at a glance. A Telegram error gives the HTTP status
and its text without a prefix, because the telegram: prefix names the
service. The behavior of the logs does not change.

Issue: e4acfcb