Add withdraw subtask to account task

[havan]

This PR adds a withdraw subtask for the account task that can be used to call withdraw function of a CM Account.

[VjeraTurk]

@havan

Is it possible to somehow check the maximum withdrawable amount?

Can you also add the unit to the description of Amount to withdraw

OPTIONS:

  --amount      Amount to withdraw 
  --cm-account  CMAccount address, default: CMACCOUNT_ADDRESS env variable 
  --private-key Private key to use, default: CMACCOUNT_PK env variable 
  --recipient   Recipient address 

withdraw: Withdraw funds from CMAccount

[havan]

Is it possible to somehow check the maximum withdrawable amount?

Not easily. We need to update the logic of the CM Account implementation.

Also, after the prefund amount is spent, then the max withdrawable amount is always the balance of the CM Account. So, I don't see a reason to implement this.

Can you also add the unit to the description of Amount to withdraw

I've added the unit param. Default is aCAM (wei) if no --unit param is given.