Use more convenient path objects

[julianhoever]

Currently, the ElasticAI.Creator uses custom path objects (InProjectPath, OnDiscPath, ...), which are not very intuitive and easy to use based on user experience. Therefore, we should replace these custom path objects with a more standardized path structure (e.g. pathlib.Path) if possible. This should make the ElasticAI.Creator more understandable.

[glencoe]

Tbh... i'd like to go even a step further and use something like a registry for architectures/entities. Each architecture/entity specifies a default name and before we produce code or in the moment an architecture/entity gets registered, we automatically generate the correct name (to avoid collisions). Then independently from that we can let an algorithm run over that registry and generate file paths and write the content there.

This way, developers would not have to worry about name collisions and we'd be in control about where/how resulting files will be stored.