* add get set methods for swap reward indexes
* add get set methods for swap accrual time
* tidy up location of multi periods
* add swap reward periods to params
* add initial legacy types for incentive
* minor refactor of migration code
* add incentive migration for swap params
* minor incentive test refactors
* add math methods to RewardIndexes
* add keeper method to increment global indexes
* add swap keeper to incentive keeper
* indicate if pool shares were found or not
* add accumulator to compute new rewards each block
* accumulate swap rewards globally
* remove unecessary keeper method
* expand doc comments on accumulator methods
* test precision not lost in accumulation
* minor fixes from merge
* rename storeGlobalDelegatorFactor to match others
* fix migration from merge
* fix bug in app setup
* fix accumulation bug when starting with no state
* rename swap files to match others
* add swap accumulation times to genesis
* remove old migration refactor
* minor updates to spec
* add high level description of how rewards work
