SDK: Need SDK "submit TX" functionality to be decoupled for use with Ledger app (TX signing)

[jurevans]

UPDATE This is addressed by namada-net/namada#1498 and is currently in testing

In order to utilize the signing feature of the Ledger Namada app, we would need to be able to sign a transaction outside of the SDK for these accounts, as private keys stay within the context of the Ledger device.

If we were to split the current SDK submit transaction functionality into the following steps, we could utilize the signing provided in the Ledger app, and still use the SDK to submit the transaction:

1. Prepare transaction data (the data to be signed)
2. Sign Tx (either use Namada SDK or Ledger Namada app)
3. Submit Tx

Note This blocks issue #253 (only on the issue of signing with the hardware wallet)

[jurevans]

Closing this, as this has been completed!