Replace Autofac

[patriksvensson]

We're currently not using any advanced features of Autofac (to my knowledge), so we should investigate whether or not we can move to something more lightweight (perhaps the homebrewed DI container we use in Cake.Frosting?). I suspect we could reduce the load time for implicit bootstrapping by doing this.

Any investigation of this needs some kind of benchmarking to make sure we're not making it worse (or replace something without an improvement).