Allow utility.batch calls

[jack-kearney]

Hey!

I noticed that utility.batch calls aren't currently supported in this application -- I've been using these in a lot of places and would love to continue using them.

I understand that utility.batch calls have the potential to introduce a lot of complexity in the signature approval process -- I think this can be improved by:

• Rejecting embedded utility.batch calls
• Limiting the number of calls in a utility.batch to a fixed constant (e.g. a max of 20 calls could be added)
• Allowing some process to configure which fields require an explicit approval (e.g. some users may not care to approve the spec version)

[jack-kearney]

I think allowing a user to upload a configuration file is a very flexible approach here. This file could:

• Allow / reject certain types of calls
• Allow whitelisting of addresses for certain calls (e.g. allow any account to transfer funds to a particular address)
• Automatically approve certain call types or calls with specific parameters
• Aliases for accounts (e.g. display cold-storage instead of a Polkadot address)

In order to update a configuration file a user would have to approve the hash of the file being generated. Ideally, this person could verify the hash matches the expected contents of the file on several devices before approving.

The only concern I have with this approach is that the schema for this configuration file could become extremely complicated. If we go down this route, we should take care to keep it this schema as simple as possible.