Fix config issues

[kueblc]

Which issues are addressed by this Pull Request?

#22, and several unreported issues:

• Client config placeholders do not represent defaults
• Required config is too strict, many options can be passed via payload
• After error, client will not have listeners set up

What does this Pull Request change?

• Respect client config.interface
• Show defaults as placeholders on client config
• Do not enforce device/interface on read/write nodes, as these can be passed in
• Set up client listeners when instantiating a new client

Does this Pull Request introduce any potentially breaking changes?

• No breaking changes, only fixes with this PR