add total supply to token storage

[tzemanovic]

We should add the total supply to the token VP to avoid iteration to calculate inflation (the VP can simply reject any changes to it in a transaction as only the protocol can mint tokens). This is needed for inflation system, see #230 (review)

[cwgoes]

@brentstone perhaps this is covered as part of the proof-of-stake inflation work?

[brentstone]

@brentstone perhaps this is covered as part of the proof-of-stake inflation work?

Yes, didn't notice there was an explicit issue for this. It is in #714.