Add support for watch wallets

[gz-c]

Watch wallets only contain addresses/public keys and do not contain seeds or private keys.

We can create wallet files with the type "watch". This wallet will not be able to perform any signing operations or generate new addresses automatically.

There are multiple ways we can create a watch wallet:

• Import a list of addresses
• Import a list of public keys
• Generate addresses from a seed one time, and discard the seed
• Import an exported watch wallet file, exported from a deterministic wallet

[gz-c]

This requires a written plan since there are multiple approaches and also involves UI changes.