sequencer rotation support

[mtsitrin]

• [x] manage activeSequencer and nextSequencer for a rollapp
• [x] manage notice_period for unbonding sequencers
• [x] emit rotate_sequencer event
• [x] expect and handle “lastBatch”
• [x] complete the sequencer rotation
• [x] #1025

phase 2:

• enforce state_update_timeout (#927 )
• enforce final_state_update_timeout (#1085 )