Add system.skills getter to actor datamodel

Intent

Add system.skills getter to actor datamodel. This reads all skillItems on an actor and returns an array of objects for skill level, base, and mods:

{
  "basicTech": {
    "level": 4,
    "stat": 6,
    "mods": 0
  },
  "meleeWeapon": {
    "level": 0,
    "stat": 6,
    "mods": 2
  }
}

These can then be accessed with actor.system.skills

---

• This is meant for a hotfix
• This is meant for the next release (see milestone)
• This needs more reviewers than normal; there may be controversy or high complexity
• This intentionally introduces regressions that will be addressed later
• There is/will be documentation changes on the wiki
• Please do not send commits here without coordinating closely with the owner
• This is a Build System change

How to test

1. Checkout/build/load
2. Create a Character/Mook
3. Adjust some Skills
4. Add some custom Skills
5. Find the actor's id
6. Run game.actors.get("ActorId").system.skills