Add DLL Loader Layer to Support Backward Compatibility

[planetchili]

By shipping the middleware DLL with the service instead of the client, we ensure that middleware-service compatibility is always guaranteed. Middleware-client compatibility is already guaranteed via C-API contract (this will be hardened/made absolute).

This change requires that clients locate the DLL at runtime and load it dynamically. To facilitate this process, we add a thin Loader Layer DLL that clients can link to with a convenient import .lib, which will transparently locate the middleware, load it, resolve all the function addresses, and forward the API calls.

• POC of loader layer DLL
• Ability to resolve mangled C++ endpoints for internal usage
• Update installer to ship middleware with service, provide loader in SDK
• Implement error checking with new PM_STATUS codes for DLL issues
• add version check mechanism in C-API, loader checks during loading
• Make loading process thread-safe
• Review and implement DLL Main hooks as necessary
• Clean out unused classes / projects (MockMiddleware etc.)
• Repair and prune API2 tests
• Cleanup organization of loader and solution project dependencies
• Update documentation