Support dynamic validator set changes about codechain

[sgkim126]

I think this can be done in three steps.

• Implement delegation of a stake to a validator
  • Delegation to none-validator is an invalid transaction in this step.
• Make a validator become a proposer in proportion to the delegated stake.
• Make a stakeholder be able to delegate their stake to anybody.

[sgkim126]

@foriequal0 Please make the delegation to the invalid validators a syntax error.

[sgkim126]

@foriequal0 Don't forget that we should support both of the current static validators and new dynamic validators.
I think you should add a new field to CommonParams to distinguish the validator configuration.

[foriequal0]

WIP

• Term change (#1508, #1519, #1537, #1552)
• Nomination (#1445)
  • Self-nomination
  • Expiration
• Punish
  • Ban
  • Jail
• Election
  • Election
  • Validator selection
  • End of term

TODO

DONE

• Module Outline (#1536)

[sgkim126]

#1574 closes it.