Part of #2454 - Add ability to transfer an account from one wallet to another

I have some wallets with "too many" accounts in them. Most of these accounts are not used anymore, so they don't need to be included in my normally active wallet. So, it would be very useful for wallet management if there were a way to split a wallet into two wallets, with the ability to select which wallet different accounts should go into. It should also be possible to remove accounts from a wallet.

Wallet management in general needs an overhaul badly. Some of the issues that I and others have brought up caused by having "too many" accounts, could be mitigated or addressed more easily if there were better wallet management capabilities.

No files, tests, or entry points are named. Start by locating the wallet-management UI and its account-selection flows, then determine how wallet transfers and account removal are represented. Done should allow selecting accounts for another wallet and removing accounts without losing them.

Written by the indexing model from the issue text.