Multi-client testing requires more portable formats, and SSZ is
much better specified than our flavour of Json.
Tools like ncli and zcli can be now used to inspect the contents
of the SSZ files.
* On the testnet site, the first N instead of the last N validators
will be considered reserved for users
* The number of validators is consistently named `totalValidators`
in all commands
* Proper keys are generated by default in validator_keygen
