Track experiments metadata

[eu9ene]

Just copy config.sh on start of every experiment to check later what datasets and parameters were used.

We might also add any useful experiment metadata to metadata.json. For example, commit hash.

Proposed directory structure:

├ experiments
│   ├ ru-en
│   │   └ experiment-name
│   │        └ metadata.json
│   │        └ config.sh