Refactor Configuration implementation to be more consistent.

Previously, accessing subsets of Configuration objects resulted in
callers receiving Map or Property objects back.  This commit makes it
possible for callers to work with Configuration objects in all
instances.

Additionally, encrypted values in Configuration objects can be handled
within a subclass of Configuration using a fluent API rather than being
handled by an outside class.
This is one of the times I wish git would've recognized that you renamed EncryptedValueConfigurationParser :) to show what it transformed into. Still looks nice.