Add comments to default configuration

[wenkokke]

• Create data/default.yaml with default configuration.
• Add to extra-source-files.
• Embed into executable using file-embed
• Add explanatory comments.
• Parse the embedded ByteString and use its value to populate the Default instances.

[wenkokke]

Most of this issue has been implemented. The only remaining thing is to add more detailed explanations to the various fields.