Account Abstraction - Spending Limits

[julio4]

Issue(s): Close #230

Description

Account Contract with Spending Limits for any ERC20 token.

[julio4]

We need to figure out the best way to correctly track allowance and spending:

When counting spending against a limit, there are two operations to track:

• approve: Allows another address to spend tokens
• transfer/transferFrom: Actually moves the tokens

Issues:

• An approval might never be spent (user approves 100 tokens but spender never uses them), but because of transferFrom we want to count it towards the spending limit (as we have no way to add our custom blocking logic when another contract call transferFrom with allowance).
• The same tokens should not be counted twice (user approves 100 then transfers 100 - shouldn't count as 200 towards the limit)