reactive-mongo: replaced val by lazy val for collection initialization
remove defunct resolvers for Datomisca
generalize collection type for find and findStream in AutoSource trait

- nothing more precise than TraversableOnce is really needed
- propagate changes to Datomisca and ReactiveMongo
- clean up a few implicits in ReactiveMongoAutoSource
Merge pull request #20 from dwhjames/topic/find-TraversableOnce

Use more general collection traits in AutoSource trait