* extract borrow sync logic into separate func
* fix borrow reward calculations
Use the normalized borrow as the source shares in reward calculations.
* extract supply sync logic into separate func
* prepare to fix supply reward calculations
* fix deposit reward calculations
Use the normalized deposit as the source shares in reward calculations.
* extract usdx sync logic into separate func
* prepare to fix usdx reward calculations
* fix cdp reward calculations
Use the normalized cdp debt as the source shares in reward calculations.
* fix compile error from messed up partial stage
* Fix incentive usdx reward bug (#976)
* minor test refactors
* fix overpayment bug
Init methods should not read params.
Add test to cover bug
* fix typos