Log into file

The logger shall be extended to allow logging into files, too.

This is meant for debugging in the ActiveWorkflow environment to be able to

• view the complete log
• view the log during process execution

Additionally, the option for rolling log files shall be evaluated and planned in a new issue.

DoD

• Logging into file is implemented - with same log level as for console
• Logging into file can be switched on via environment parameter
• Target directory for log files can be set via environment parameter
• Rolling log files are planned and a follow-up issue is created