Implement burnsale for vCHI

[domob1812]

This implements logic to mint vCHI through burning CHI, i.e. "buy in a burnsale". This is not a normal token sale, as the proceeds get burned, rather than being paid to the Xaya team (or anyone else for that matter). It is a truly decentralised and fair distribution of vCHI.

There is a maximum supply of 50B vCHI that can be bought that way, with increasing prices the more get bought. The sale will start with the 0.3 competition, but will carry on into the launch of the full game (i.e. burn-sale and in general vCHI moves will be kept running and not reset, while all other parts of the game will of course be reset).

To initiate a buy, a move like this with an explicit request has to be sent:

{"vc": {"m": {}}}

In addition, CHI must be burnt to g/tn. Then a corresponding amount of vCHI will be minted, depending on how much was burnt and what the current burnsale stage is.

[domob1812]

Also includes a bump of the maximum allowed vCHI amount in moves to 100B, which will be the total supply. And requires Xaya Core 1.4.0 or up, which implemented burns first.

[domob1812]

This adds a new RPC method getmoneysupply (and a matching moneysupply field in the full game-state JSON), which reports some data about the vCHI money supply, and in particular details about the ongoing burnsale.

Furthermore, the accounts in the game state now keep track of two balances: The normal one as before, and a minted field, which just tracks the minted vCHI, which corresponds to what will carry over into the full game.