Create configurable logging destination for C-coded modules

[ReneWassinkAlliander]

At present the destination of all loginfo is hardcoded to syslog. However in container-environment the syslog functionality is not available by default. It would be useful to have the option to output the logging to stdout.

[MarkRiddoch]

This is a particular problem for Docker as it does not support the standard Linux logging mechanism. It would be relatively easy to make a change to the Logger class to implement this. Standard output is not a good option in general however as Fledge is designed to be used unattended. We can look into the best Docker solution.