improve configuration process

Sketch of the new configuration process:

• use Properties to store and read the configuration parameters.
• read external configuration properties file (either local path or via command line argument).
• provide a default configuration as resource within the executable jar.
• if there is no external configuration file present, write out the default values.
• re-read properties when file changes; only between module runs (this is after the implementation of the scheduler, #19018 (moved))
• use enum as keys

Questions to decide:

1. property format: XML or plain properties (the latter might be more readable)
2. default value settings