Make iterating through delegators in staking contract more efficient

[joshuahannan]

Issue To Be Solved

There is a lot of code in the staking contract (FlowIDTableStaking) that iterates through a node's delegators and does something. This could be better.

Example

Suggest A Solution

• Use a utility function that uses an iterator or something like that to cut back on the boilerplate required for iterating through delegators