spl-token-cli: No way to look up mint by account

[t-nelson]

Problem

spl-token-cli has no way to directly look up the mint associated with a given token account. One can find this information by providing both the the token authority pubkey and account address, but this is cumbersome.

Proposed solution

1. Quick and dirty. Add a --verbose flag to balance which additionally displays the mint address. This feels a little overloaded
2. Add an account subcommand that displays all fields for a given account. This would be more flexible for CLI wrapped automation, especially if we add support for --output-format=json in the future.