Support database configuration

[sweetlandj]

We should create an IConfigurationProvider abstraction with multiple implementation such as:

• AppConfigConfigurationProvider -- reads from app.config or web.config
• SqlConfigurationProvider -- Reads and configuration from database
• HttpConfigurationProvider -- REST API for reading config as a JSON document
• (etc.)

In the future we might want to consider an IBus shim implementation that will "phone home" and update its configuration (creating a new bus instance) and then swap out the old instance for the new instance when configuration changes in a way that is transparent to any consumers o the IBus interface.