group query for validation according to a queryLimit

Hej @fwbrasil

I did a implementation of a query limitation. But there are some open points we need to discuss.
Firstmost my implementation affects the return type and has thereby influence on https://github.com/fwbrasil/activate/blob/master/activate-jdbc-async/src/main/scala/net/fwbrasil/activate/storage/relational/async/AsyncPostgreSQLStorage.scala#L168-L187
My Question why does that method expect a Future[Unit] as return type and what does your foldLeft do there?
I would do something like: 
````
val results = for(query <- query) yield future(query)
val result = Future sequence results 
 
````
The second question would be what kind of limit would you see as sensible?

Mailinglist thread: https://groups.google.com/forum/#!topic/activate-persistence/AtHMiWCz1NM