DelegatorStartingInfo queries the starting info for a delegator.

DelegatorStartingInfo represents the starting info for a delegator reward period. It tracks the previous validator period, the delegation's amount of staking token, and the creation height (to check later on if any slashes have occurred). NOTE: Even though validators are slashed to whole staking tokens, the delegators within the validator may be left with less than a full token, thus sdk.Dec is used.