Add "Max" option in escrow amount selection

[kyrers]

When the user is selecting the escrow amount, a "Max" button should be available for convenience. If clicked, the escrow amount becomes the wallet's available balance for the selected token.

Note that this requires knowing the wallet balance for the selected escrow token, so if the user inputs an amount greater than the wallet balance, the "Next" button should be disabled, and the user can't proceed to the next step.

Additionally, if the selected escrow token is ETH, some calculations are needed because transaction fees will need to be paid in ETH.