Properly support deposits of custom base token in Portal

[popzxc]

Right now, running the portal for the chain with custom base token works, but it has some quirks.
One of those quirks is the need for double token approval: when estimating deposit fee, seemingly the need to transfer the base token on L1 is not respected in allowance calculation.

The correct flow would be:

• Add L2 fee in base token estimation on the deposit view
• Display that second fee to the user
• Add up that additional fee value in the allowance approval
• Use that fee value in the deposit method

In order to test the implementation, you need to deploy a chain with custom base token (use zkstack CLI tool for that, documentation).

The outcome of this task: the flow to deposit custom base tokens is no different from ETH deposit flow (from user perspective).