Configs refactor

Makes it easier to write config files in the future.

Check the changes files for the new syntax - the keyword `"fileUrl"` has been replaced by "@include" and the stable part of the path is defaulted now.

`arethusa-cli`' supports this since version `0.1.0`


Several parts of conf files have been moved to own directories to encourage reuse. The `perseids` configuration files do so already.