Use more general collection traits in AutoSource trait

I think the return types of `find` and `findStream` are over specified.

```scala
def find(…): Future[Seq[(T, Id)]]
def findStream(…): Enumerator[Iterator[(T, Id)]]
```

Do any of the Autosource controller implementations actually require anything beyond `TraversableOne` (to replace `Seq` and `Iterator`)? The Datomisca implementation certainly doesn’t.