Feat / Add Uniswap to gateway

[fengtality]

I added a commit which:

• Addresses https://github.com/CoinAlpha/hummingbot/issues/2656: moves the Balancer and Uniswap addresses into their respective files, so we can delete the EXCHANGE_PROXY and UNISWAP_ROUTER constants in the Gateway installation script.
• Uses the number of swaps utilized by Balancer to set the gas limit dynamically. The Balancer price and trade functions now have an optional parameter maxSwaps that sets the number of swaps used.

Smaller traders would use a small maxSwaps number because they care more about gas costs, while larger traders would use a high maxSwaps because they want the best price and don't care about gas as much. We should factor this calculation into the client profitability calculation as well:

const GAS_BASE = 200000;
const GAS_PER_SWAP = 100000;
const gasLimit = GAS_BASE + MAX_SWAPS * GAS_PER_SWAP

[fengtality]

Sorry @vic-en for trampling all over your PR... I should have created a separate branch for the last 2 commits. I don't think they affected the Uniswap part of the code, but feel free to roll them back if you want.

I think the buy function in Uniswap may still throw an error, though I was testing using Postman and not with the client.

[vic-en]

Sorry @vic-en for trampling all over your PR... I should have created a separate branch for the last 2 commits. I don't think they affected the Uniswap part of the code, but feel free to roll them back if you want.

I think the buy function in Uniswap may still throw an error, though I was testing using Postman and not with the client.

I figured it. I'd push a commit to address that.