Crossbow animations blending is buggy

1. Currently in both vanilla and OpenMW there is a twitching when actor starts or stops walking during crossbow reload animation. That's because of animation blending (crossbow reload + walking/standing provides very different result).
2. Crossbow position is weird in the 1st-person mode when idle or jumping. It is a OpenMW-specific issue. That's because crossbows do not have own idle animation group, so they use default idle/jumping animation group as fallback.

Possible solution for these issues:

1. Apply crossbow reload animation only for upper body.
2. Use 1h idle and jumping animations as a fallback for crossbows.