Need the ability to manipulate the response from Om Server API

[awkay]

Om mutations like login should be able to affect responses. For example, we should be able to add cookies, other headers, change the status code, etc.

I'm suggesting that top-level queries and mutations be able to return a response like this:

(defn some-mutation [env k p]
   (response-with-status { :tempids {n m} } 202))

and have that (probably through metadata) affect the underlying response to the client.

[wilkerlucio]

I just found myself needing it as well to change the :session.

[Pancia]

Merged in #20