Enable spinning additional nodes

[norswap]

I think we should have additional configuration options for spinning additional "regular" nodes besides the sequencers.

These options should generally follow that of the sequencer, but be arrays instead. These arrays must be checked to have the same size. If they are empty, no additional node will be spun.

Each of these nodes also needs an execution engine, so a similar setup should exist for the engines. Here there is a question of whether to separate the execution engine that will be used by the sequencer, and those that will be used by the extra nodes. It seems not separating them out reduce code duplication.

Maybe that should be the case for nodes too? With an option to designate if a node (if any) should be the sequencer? Maybe simply a boolean flag that says whether the first item in the array should be the sequencer.

This blocks #68

[GrapeBaBa]

@thinkAfCod Can you have a look?