FIx: stakingReward documentation/naming issues

[dkent600]

1. Here:

contracts/contracts/incentives/StakingRewards.sol

Line 54 in 6b58c0d

* @param _duration Duration of the staking in days

The explanation for duration is incorrect. We added isActive for a reason, which is that duration does not suffice to compute the "duration for staking". Can we please provide a correct explanation for how duration is used?

2. Here:

contracts/contracts/incentives/StakingRewards.sol

Line 55 in 6b58c0d

* @param _avatar Address of reward distribution recepient

Must the _avatar be an avatar? If not, can we rename this? See the following 3):

3. Here:

contracts/contracts/incentives/StakingRewards.sol

Line 79 in 6b58c0d

rewardDistribution = _avatar;

The entire rewardDistribution nomenclature seems to make no sense. First, it is not a distribution, it is an account. Second, its use has nothing to do with who gets rewarded nor how rewards are distributed. It is only used to identify an account that can invoke a couple of functions. Wouldn't it make more sense to call this something like controller or admin?

4. Having said 3), it is super unclear what notifyRewardAmount does. It is external, presumably meant to be invoked by rewardDistribution. Can we document this function?