Unify CLI parameters

[dknopik]

We have, as of now, 3 subcommands. Some share options, such as the network to connect to for node and the online mode of keysplit.

It would be nice to unify the infrastructure for the shared CLI parameters, by having some kind of shared options struct that is valid for every subcommand. This allows for clearer code reuse and makes the CLI more consistent across subcommands.

[dknopik]

Unfortunately un-scoping this from v0.1.0 due to lack of time - This is mainly a technical improvement providing almost no user value, except for the secondary commands.