New "chain mode" configuration option

[jeffsmale90]

In some cases Ganache functions differently to Geth, see: #2176, and it makes sense to continue to do so as a default.

Users may want to run Ganache configured in such a way that it more closely matches Geth.

This issue covers introducing a "chain mode" configuration option so that the user may specify something like -chain.mode=geth (this allows for different compatibility modes to be introduced in the future.

This could set default configuration values, as well as expose a flag internally that can be used to derive non-user configurable behaviour.