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.
If you don't want hard-coded magic numbers and document constants properly I suggest the following:

```csharp
[Desc("Number of ticks to wait until decreasing the effective move radius.")]
public readonly int MoveReductionRadiusScale = 10;

[...]

if (++ticksIdle % info.MoveReductionRadiusScale == 0)
```