WebMail Configuration Scheme
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WebMail has a new configuration scheme since v0.6.0.
Program parts can register configuration parameters with the main configuration scheme.
It is also possible that objects are notified on configuration changes so an appropriate
action can be taken. This works much like Java's AWT Listeners, so the corresponding
interface is called ConfigurationListener.

Unfortunately, this decentralized configuration doesn't allow a effective central 
compile-time configuration any longer. Therefore, there are some system properties
that can be passed to the WebMail startcommand. Mainly, you will need to use
--data-path, if your configuration file cannot be found in the default place.

The telnet administration interface will be replaced soon with a HTML configuration form
that is dynamically generated from the configuration parameters.

Currently there are three types of Configuration Parameters:

- String-parameters: These can take any value
- Choice-parameters: can only take certain allowed parameters
- YesNo-parameters: can only take "YES" or "NO" as value and are just a specialized
                    version of the choice parameters.

Each configuration parameter must be registered with a unique String key 
(name of the parameter), a short description to be used as help text in the 
administration interface and with a default value if not yet set by the user.