Reactive Slick

Here's the ongoing work on Reactive Slick.

/cc @cvogt for review later
Hi, you can use this kind of tricks if you want to omit type casts from your code base:
https://github.com/playframework/playframework/blob/master/framework/src/play-functional/src/main/scala/play/api/libs/functional/Functors.scala#L46-L67