Authorities should cap relay consensus weight as a new consensus method

arma says on IRC:

armadev: teor4: is there a ticket for capping the total weight a given relay can get? i remember you mentioning that this should happen as a new consensus method, i.e. so the authorities actually collectively cap it, rather than relying on each vote individually to do it. i think that's a compelling idea.

I'm not sure if the cap should be the same across the network, or if it should be different based on each relay's MaxAdvertisedBandwidth.

If we want to base it on MaxAdvertisedBandwidth, we should also make MaxAdvertisedBandwidth a separate number in relay descriptor bandwidth lines, rather than combining it with bandwidth rate and bandwidth burst.