Reactive Slick

Here's the ongoing work on Reactive Slick.

/cc @cvogt for review later
Alright. So (IMHO) either it doesn't need an EC, in which case it is OK to use a NoOp EC, or it needs an EC and then it needs to be specified from the outside. Using `global` with no way of changing it is dubious at best and dangerous at worst, I've seen a lot of bad things happening, much so that I am nowadays considering adding `global` as a mistake (even though I was the one who created it).