[#1364] Move skills to top level of system data

[JPMeehan]

1. We've got more general need to have it be skills.value so there can be the already-prepared skills.list and skills.modifiers
2. While normal NPCs don't have skills, there's enough other actor types like Companions that have skills. This also jives better with our expected Follower data.

[krbz999]

Good idea, but let's add shims to AEs with deprecation period until 1.0.0.