Allow to overwrite config-default on per-server basis

[Krzmbrzl]

Config defaults like name-prefix and -suffix as well as server-mods should be overwritable on a per-server basis.

Example
I'd like to be able to set my config to prefix: "MyPrefix" and then this prefix is used on all servers, that don't explicitly overwrite this behaviour.
But it should be possible to overwrite it, so that each server can have its own prefix (if desired).

The same applies for the other options mentioned above.