Make ganache-core/cli interface more adaptable and less invasive

[mikeseese]

Since Velma is a real-time debugger, every step event needs to be processed to determine if it's a breakpoint/etc. At first the VM/ganache interface to Velma was a websocket connection, but this was way too slow. So now Velma<->ganache/ejsvm (ethereumjs-vm) need to have in-memory communication (IPC hasn't been tried yet to keep things simple and in-memory [aka the same process] has worked thusfar) has been used.

The current implementation adds sdbhook.js (Velma used to be called Solidity Debugger [aka sdb] before release) to ganache-core to add the necessary extensions support for handling these VM events.

This issue proposes the following changes:

• Remove sdbhook.js from ganache-core
• Add some sort of extensibility API for node modules to listen to these events through ganache-core (aka maybe just adding an event emitter that re-emits events, with maybe some nice structure)
• Move most of the sdbhook.js functionality into Velma