Ship Akavache 4.0

This branch is the Master branch for tracking all of the stuff that will eventually become Akavache 4.0

## Cool Ideas

## What has shipped

* Remove dependency on ReactiveUI (#99)

## Breaking Changes

* If you expected things to become synchronous in the test runner when using Akavache, it might not now unless you're also using RxUI 6.0. Probably nobody cares though about this