[th/keyfile-public-api]
The first part of the branch reworks the keyfile code to make it more suitable for exposing it as public API.
The second part exposes keyfile API in libnm. Note that the second part is blocked by the relicensing effort in !390 (closed). The second part won't be merged before that is fixed, however it's useful to see how it would look at the end.
Please review.