Factions API for Lua

What should be done:

1. A way to get/set a rank in given faction for given player.
2. A way to expell player/NPC from faction and return him to faction.
3. A way to get/set reputation with given faction.
4. A way to handle factions for NPCs (for Morrowind content they have only a "primary faction", stored in ESM record).

At least pt. 1 is needed for perfect placement mods (with !2949 (merged) it should be enough to check if player is allowed to interact with selected item).