Support Ledger devices via Zondax app

[jurevans]

We need to support connecting to the Ledger Nano S+ device via the Zondax integration.

See https://github.com/Zondax/ledger-namada

• User can choose to connect their Ledger device
• User is prompted to unlock their Ledger device if needed
• User is directed to a connect to Ledger flow (See: https://support.ledger.com/hc/en-us/articles/4404366864657-Connect-your-Ledger-to-Metamask for an example of what this looks like on Metamask - similar to Keplr)
• User can access accounts on their Ledger device
• Test transfer transaction signing using keys on their Ledger device
• Block PR merging until murisi/separate-signing is merged to Namada (See Murisi/separate signing namada#1498)