support sequencer rotation

[mtsitrin]

Full node:

• [ ] remove ABCI validators related logic
• [ ] Load sequencerSet on init
• [ ] manage ActiveSequencer in state
  • [ ] validate blocks with this pubkey
  • [ ] update ActiveSequencer from block header after block commits succesfully
  • [ ] Halt in case of no sequencer
  • [ ] Change to aggregator if needed

Sequencer part:

• #949

• [ ] Integration with Hub

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Phase 2:

• more hermetic rotation event - add flag in stateUpdateResponse, and query rotation state on reboot
• role switch from sequencer to full node
• role switch from full node to sequencer

Phase 3:

• refactor sequencerSet management (by event/from block)

• [ ] enforce max_uncommited_state_time
• [ ] support proposer_rotated event, to recover in case of halt