Allow sending logging to stdout/stderr instead of app/log/...

[raboof]

When deploying providence in a container, it would be convenient if we could configure it to send logging to stdout/stderr instead of to log files in under app/log. This would allow whatever logging driver is configured for this container to pick up the logging (e.g. https://docs.docker.com/config/containers/logging/).

I see providence uses a pre-1.0.0 version of KLogger (https://github.com/katzgrau/KLogger) for the logging, which currently does not seem to make it easy to log to a single file rather than to a directory.

I see a couple of ways forward:

• Add this feature to the KLogger library included in providence (not very nice since that'd mean diverging from upstream)
• Add this feature to the upstream KLogger, then upgrade providence to use that version (this looks like it'll require some code changes, since KLogger has since switched to PSR-3, though I haven't checked how much)
• Switch to a different logger library altogether

(this is not a high-priority issue for me, but it'd be nice to discuss the way forward a bit so when the time comes we know what to do ;) )

[collectiveaccess]

I believe that changing the logging library and standardizing how logging is done is the way to go. Currently, for historical reasons (don't ask) some logging is done by KLogger, some by Zend Logger and some into a database table (ca_eventlog) Cleaning up that (minor) mess would have to be part of this.