staking: inventorize useful ABCI events to index

[zbuc]

The staking component has minimal event indexing (delegate and undelegate as of now).

Similarly to #3645 we should enumerate useful events to index (state transitions and such) and implement.

[zbuc]

Events to index:

• [x] Delegate
• [x] Undelegate
• [x] Undelegate claim
• [x] Validator definition change
• [x] Validator state changes
• [x] Validator rate/power/delegation token supply changes during end_epoch
• [x] Validator missed block
• [x] Funding stream reward payouts
• [x] Slashing penalties applied
• [x] Bonding state change