* Add accumulators
* Move accumulator back to keeper package
* Add earn specific accumulators
* Move store methods to sub-package
* Move earn accumulator
* Rename accumulator files
* Add store doc comment
* Add earn accumulator tests, panic if accumulator not used with earn claim type
* Update earn accumulator tests to use new methods
* Add staking test for earn accumulator
* Add test for accumulator proportional rewards
* Remove old copy of GetProportionalRewardsPerSecond
* Add test for basic accumulator
* Fix AddIncentiveMultiRewardPeriod replacement
* Deduplicate base earn reward accumulator
* Check errors in tests
* Validate RewardPeriods in Params.Validate()
* Use adapter to fetch earn total shares
