Add helper functions for user incentives data

[defispartan]

Add functions to src/formatters/incentive:

• calculate a/v/s incentives for an individual UserReserve (calculate-user-reserve-incentives)
• calculate totalRewards for a user (calculate-user-incentives-summary)

Input types based on https://github.com/aave/protocol-v2/blob/c786b246ccdb58537b0f8b61dbb23a6b409baa12/contracts/misc/UiIncentiveDataProvider.sol