Store total supply along market fee

[oberstet]

When a new market is created, the market owner will set the fee rate that applies within the market using an absolute token amount that is to be related to the total token supply at that moment!

However, for tokens with a non-fixed supply, the total supply can change. Hence we should store total supply as well, here https://github.com/crossbario/xbr-protocol/blob/2398f2a03f56fb3dd27be1a48fbd2d93ba9be347/contracts/XBRTypes.sol#L117