Allow saveload to serialize/deserialize more than 8 component types

I'm not sure if I'm doing something horribly wrong or commendably right, but I've hit the size limit of tuples that implement the `SerializeComponents`/`DeserializeComponents` traits, which is currently 8 component types.

This will not compile:
```
SerializeComponents::::serialize(
&(positions, sizes, shapes, rooms, in_rooms, player_controllers, velocities,
forces, aims, collision_sets, revolute_joints, jumps, animations),
&entities,
&markers,
&mut serializer
)
```

I think the proper solution here would be to implement `SerializeComponents` for any structure with `#[derive(SystemData)]`, but I don't know enough Rust to figure out how to do it myself.

Short-term I'd be happy with increasing the tuple size limit too.