Spec clean up.  Removing AppSettingsKeys dependency from WebConfigurationAdapterSpecs to avoid encrouraging leaky abstractions.
Adding overload to accept an IEnumerable of keys to be cleared.
Adding tests for retrieving single values.
Isolating keys and key collections so they don't depend on a single implementation.
Removing ResetDefaults() from contract.
Refactorings from ConfigurationProvider, and adding specs.  Changing default settings.