Add broker voting mechanism

[patriacaelum]

• Whitelisting mechanism that is brokers only, though how do we start? When there are no brokers, who does the whitelisting? Or is there an initial whitelist provided by the owner?
• Joint whitelisting mechanism where voting power is shared over the payers and brokers

[theoriginalMAR]

I think the owner should be the one doing the whitelisting initially. Also, what do you mean by an initial whitelist provided by the owner?