Implement build order plugin for sc2reader

Before calling `sc2reader.load_replay`, register the plugin with the engine:

```python
from sibyl.build_order import BuildOrderTracker()
sc2reader.engine.register_plugin(BuildOrderTracker())

rep = sc2reader.load_replay(...)
for human in rep.humans:
    print(human.build_order)
```

Still missing some Ability ID codes.