Feature/bcp swap

[jordaniza]

The swap modal for DEFI+S/L => DEFI++ is now extended to multiple assets, whilst requiring a single buy token.

This means we can swap:

• DEFI+L/DEFI+S -> DEFI++
• DEFI++/WETH/WBTC -> BCP

The swap modal is configured to add a flexible launcher and take a contract address. It can therefore be reused in several places as needed.

[jordaniza]

Some additional changes:

• Fixed an issue whereby styling on large screens was broken
• Improved loading feedback
• Removed entry/exit and instead added auto detect exitPool if selecting the corresponding token
• Removed the dedicated button and conditionally added to the swap if you hit swap from the BCP page.

Outstanding issues:

• The currently design of the swap modal does not pre-fetch tokens, there is therefore a loading period while tokens are being fetched. Made some changes to improve loading speed and UI responsiveness but does not seem to be a quick way around that while keeping the token list dynamic.

[jordaniza]

@Alexintosh I updated the PR based on our discussion:

• When not signed in, we still populate the tokens list, ignoring balances
• Use the exitswapPoolAmountIn contract call instead of the other one

[jordaniza]

Based on comments I have added two further changes:

1. Once the approveMax function has been called, we update the sellToken allowance:

      await approveMax(sellToken.address, spender);
      sellToken.allowance = ethers.constants.MaxUint256;

This prevents the issue whereby the user is waiting for approvals to update, straight after approving the contract.

2. Add a transaction lifecycle hook isConfirmingTx which will cause the swap button to be disabled and render Swap in Progress... until the swap resolves. This at the very least gives visual feedback to the user that the swap is happening and prevents accidentally wasting gas on a double spend