[WIP] Improved coding standards

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Related tickets | 
| License       | GNU GPLv3

- [ ] Talk about these conventions
- [ ] Clean up the commit history
Better wording:

> For sequence types (`dict`, `list`, ...) in a multi-line form, add a comma after each item, even the last one;