Part 1 of Core refactoring - Core Namespace

[capnkenny]

Please check if the PR fulfills these requirements

• [X] The commit message follows our guidelines
• [N/A] Tests for the changes have been added (for bug fixes / features)
• [N/A] Documentation has been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...) Begins to address the namespace and engine refactoring as briefly mentioned in #423

Is there an open issue that this resolves? If so, please link it here.

423

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?) Items in the core namespace (built by the NovelRT_Core target) will be linked directly in via the Engine target. This also begins to remove dependencies on NovelRT.h

Other information: One of many steps - this one was for the base implementation (and figuring out how to do it) - additional CMake changes will come later on once the namespaces begin to shape up (i.e. target OS detection, etc)

[capnkenny]

Closing, as we have discussed changing our approach at a later date (for now, MVP and splitting platform deps is going to be the main route).