Upgraded Q -> M from 413 [1656341455160]

[code423n4]

Judge has assessed an item in Issue #413 as Medium risk. The relevant finding follows:

[HickupHH3]

L07 - Adding new bonus tokens could lead to Dos
Admin could only add new bonus tokens for withdrawers using function setBonusToken().

Withdraw transaction calling to distributeBonusTokenRewards() which could run out of gas if list of bonus tokens will be too big.
This would lead to the inability of users to withdraw their assets.

Consider adding a function that allows the admin to delete addresses from bonusTokens.

dup of #249