Support more currencies in proposal payments

[jeisses]

Feature

Users should be able to select multiple tokens as payment for their proposal, like NFX or EOS, instead of just EFX.

Description

Effect DAO currently supports 1 currency as payment for a proposal. The smart contract design already supports multiple tokens but for simplicity this has been disabled. In recent DAO calls we discussed the need to allow NFX and EOS to be paid as rewards.

This proposals smart contract will need a small update to enable support for multiple tokens.

A side note on security: it should not cause much problems to allow arbitrary currencies. If someone adds currencies the DAO does not own this should be detected by the UI so people won't vote on it, and the proposal will not be able to execute anyways. There is a small risk of the spent map of the cycle to consume a lot of RAM, but this only gets populated for approved proposals anyways.

Steps

• Uncomment, finish, and thoroughly test multi-currency support in processcycle:
  https://github.com/effectai/effect-network/blob/master/contracts/proposals/proposals.cpp#L176

• Add e2e tests with multiple pays

• Implement frontend feature in effect-dao repo

[jeisses]

This feature can now be accomplished with ATPs. I actually think we can get rid of cycle budgets, proposal rewards, and recycle strategies and replace them with ATPs. We would end up with a more simple and flexible DAO structure. I'll write this out in detail soon.