Support action chaining

[nadenf]

Given the following code:

Effect.action(Http.call(url).map { result =>
  Action1()
  Action2()
}

It would be useful to be able to chain Action1 and Action2 without having to create an Action3 that combines the two.

Similar to how you have EffectSeq it would be useful to have ActionSeq so we can do:

Effect.action(Http.call(url).map { result =>
  Action1() >> Action2()
}