Refactor Platform and Sandboxes

Description

This re factor moves all of the code for sandboxes in to the sandboxes from the platform.

Changes proposed in this merge request:

• Move all sand box code in to the sandbox.
• Provide mechanism for selecting sandbox in platform class.
• Remove Unix platform.

This merge request, when approved, will contribute to: #719 (closed) and help !951 (merged)

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