`@0x/contracts-staking`: Convert all rewards to WETH.
`@0x/contracts-staking`: Style changes.
`@0x/contracts-staking`: Address misc. review comments.
`@0x/contracts-staking`: Make `LibFractions` scaling a separate step.
`@0x/contracts-staking`: Merge `exchange_fees` unit tests into `protocol_fees` unit tests.
`@0x/contracts-staking`: Remove `ProtocolFeeActor` and any use of it.
`@0x/contracts-staking`: Remove unused constants.
`@0x/contracts-staking`: Move WETH assertion constructor into `MixinDeploymentConstants`.
`@0x/contracts-staking`: Add more unit tests.