Somehow redo the chain maker with a simulated backend

[karalabe]

The chain maker is one of those relics in our code where we hacked together a "kind of" chain to run our tests against. This was kind of fine, but as our chains get more and more complex, we keep hitting annoying cornercases (e.g. some tests assume an archive mode in the chain maker). These are hard to fix, because it's not a "real chain" where I can flip a switch to change between hash/path full/archive/etc, rather these decisions are hard coded.

Would be nice to see if we can somehow gut out the chain maker the same way we gutted out the simulated backend and rather place a full geth behind it. Should be viable now with all the weird consensus engines knocked out and only the beacon chain needing support.