Update Contracts.ts TOKEN_AMOUNT

[debragail]

TODO: TOKEN_AMOUNT need to be set by basicMission contract.

https://github.com/DAVFoundation/dav-js/blob/master/src/Contracts.ts

TOKEN_AMOUNT is currently set to a constant. Should be updated by the basicMission contract.

https://github.com/DAVFoundation/dav-js/blob/master/src/contracts/BasicMission.json