Add inline gas estimates

[callil]

New users are not aware of gas fees and don't read their wallet transaction prompts. We should show the estimated gas fees inline so users can get a better idea of the total cost of the transaction.

There are two cases:

1. For a regular swap, the estimated gas costs should be displayed in the confirm screen and clearly show it is an additional Ethereum fee.

2. For swaps with approves (not permits) - we should show the estimated total transaction cost (approve + swap fee) under the buttons. This may help reduce sticker shock of the two transactions.

Additional considerations:

• Gas estimated should be displayed in ETH & USD prices.
• We should consider displaying a warning if USD prices of the fee is higher than the value of the swap!!
• Add a generalized gas tracker in the header

[jab416171]

A warning should also be added if the gas of the approve+swap is higher than the user's eth balance