There are situations where you may not want to run the HTTP server in a
full blown WSGI-over-Tornado container - unit/integration tests and
embedded single-core devices are among those cases.
In those scenarios, we should allow the user to be able to run the
backend using the built-in Werkzeug server provided by Flask.
The cron scheduler has been made more robust against changes in the
system clock (caused by e.g. DST changes, NTP syncs or manual setting).
A more granular management for cronjob events has been introduced, now
supporting a `TIME_SYNC` event besides the usual `STOP`. When the cron
scheduler detects a system clock drift (i.e. the timestamp offset before
and after a blocking wait is >1 sec) then all the cronjobs are notified
and forced to refresh their state.
