Taiga-Typhon Simple Execution Server

[isheff]

Build a single prototype server which executes transactions sent to it serially (no fancy concurrency of any kind), storing (persistent) state in memory. The goal here is to establish that our shielded and unshielded transaction model works the way we think it does, so when we go to build a fancy execution engine, we can check that it behaves the same as the simple execution server.