feat: split rewarding and slashing

This commit splits the `DoSlash` trait in two traits: `DoReward` and `DoSlash`

The reasons for it, is that we want reward based on the `total slashed amount`
but the entire amount doesn't necessarily be rewarded. Some part of the total
slashed amount might need to transmitted to some other part such as
`treasory`.

Thus, instead we return the total slash and `ReportSlashing` has to determine
what to do with the total slashed amount.

In other words, the concrete misconduct type determines what to do.