ERC20 support

[mehrdadmms]

Goal

Apart from ETH, DAO should be able to set spending limit for desired ERC20 tokens through installation.

How

• Create a mapping to store different tokens and their corresponding spending limit
• Receive token address through calldata with the spending limit
• Check DAO Action array for ERC20 token withdrawal and submit that to the DAO
• Revert on any action other than withdrawal of the configured tokens
• Update the updateSpendingLimit function to update the spending limit for ERC20 tokens as well