Refactoring: Use ConfigurationMonitor<TSection> singletons to access all configuration sections.

[jmderuty]

Always using ConfigurationMonitor<TSection> to track config sections enables:

• Discovery of configuration classes and section keys.
• Improved performance of configuration retrieval and updating

to use the new pattern:

1. make the configuration section class inherit from IConfigurationSection<T> (for instance class ConfigSection : IConfigurationSection
2. register ConfigurationMonitor in the resolver as a single instance.
3. resolve ConfigSection instead of IConfiguration in the classes which need access to the config section.