Feature: Set partial configs

[rathesDot]

One should be able to set some config somewhere in the content tree.

For example, consider having a content structure like this:

|-- de
|    |-- seite-1
|    |-- seite-2
|-- en
|    |-- page-1
|    |-- page-2

One should be able to set e.g. the apps locale to de when on the de/ branch and to en when on the en/ branch of the tree ...

[rathesDot]

If it is just for the language code, one should also work with a file suffix. Something like seite-1.de.md would be a german page, while page-1.md would be the default language, set in config/mozhi.php