Compute total supply at every block

At every block, compute the total amount of tokens on the chain. This serves at least two purposes:

1. it permits to recalibrate rewards and security deposit amounts as fixed percentages of the supply

2. it acts as a safeguard, assert that a block which creates more tokens than expected through the normal working of the protocol is invalid. This would have the effect of severely limiting the damage of any bug allowing the creation of tokens out of thin air (bitcoin in 2011 and Monero n 2017 narrowly avoided this scenario)