D2k: Sandworms implementation

Using Mailaender's code as basis, this is my implementation of the sandworm behavior. It is still WIP, but you can get an idea of how it looks from the shellmap.
This can simplify down to
```csharp
class WormSpawnerInfo : TraitInfo<WormSpawner> { }
class WormSpawner { }
```

These definitions can probably live at the bottom of WormManager.cs