Separate implementation and interface headers for Client, Dataset, ConfigOptions, LogContext

[billschereriii]

Description

We need to separate the public-facing interface portions of the headers for the Client, Dataset, ConfigOptions, and LogContext classes from the internal implementation of these classes.

Justification

This will enable two things:

1. We can limit just the public interfaces to what is shared in the install folder
2. We can stop sharing third party software interfaces and libraries in the install folder

Implementation Strategy

We can make classes that define the interfaces and share the headers for them. We can then make our implementation classes derive from the interface classes.