Proper unlock wallet error/notification when using a wallet related commands

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## The Issue
Currently, if you call a command that requires the wallet to be unlocked, you get the below feedback from the daemon (and the command stops). On the desktop app, we force users to unlock the wallet on startup, but it would be nice to provide an option or allow unlocking only when wallet related commands are run.

App developers will need a way to consistently tell when a wallet needs to be unlocked, wait for the password, and then proceed with the command execution. This would most likely require a specific error code (see https://github.com/lbryio/lbry/issues/1134) to then trigger the user for their password. After entering the password, the command should continue executing.

```
lbrynet-cli get one
ERROR: your wallet is locked
```
```2018-09-11 12:19:39,584 INFO lbrynet.core.Wallet:858: Waiting for wallet password```

## System Configuration

- LBRY Daemon version:
- LBRY App version:
- LBRY Installation ID:
- Operating system:

## Anything Else

## Screenshots

Start with the `lbrynet-cli get one` entry point and the daemon's wallet-locked response described in the issue. Trace how wallet-related commands report the locked state and how the app could distinguish it from other failures. Done should include a consistent unlock signal and command continuation after the password is supplied.

Written by the indexing model from the issue text.