Enhance conf mechanism

[hebasta]

Right now there is a basic configuration file which can be overwritten with a new config file (by running the jar with the according filename as argument). Default configuration values as backup are part of the sourcecode.

Regarding, that we have several different instances in Kalamar (and have sometimes only slight changes like different footers in the RTF files) we should enhance the conf mechanism:

• the default conf values should be evaluated and changed if needed
• overwriting only single properties should be supported
• ENV variables (see Kalamar) should be considered