Can not get tags for knot that accept parameters

I believe it is a bug because I am unable to obtain tags for a specific knot when it accepts parameters. When it does not take any parameters - everything works fine.

I've managed to do a quick workaround in `Story.cs` around line 2391

**Original:**
```
List tags = null;
foreach (var c in flowContainer.content) {
var tag = c as Runtime.Tag;
if (tag) {
if (tags == null) tags = new List ();
tags.Add (tag.text);
} else break;
}

return tags;
```

**Modified:**
```
List tags = null;
foreach (var c in flowContainer.content.Where(item => item is Runtime.Tag)) {
var tag = c as Runtime.Tag;
if (tag) {
if (tags == null) tags = new List ();
tags.Add (tag.text);
} else break;
}

return tags;
```

It is caused how content is organized. When there are parameters in the knot the first object in flowContainer.content is of type VariableAssignment and thus the flow breaks and null list is being returned.