add scene graph and higher level scene object API

[gituser12981u2]

BREAKING CHANGE: now one must instantiate objects for the scene graph with scene object in scenes

Description

Added a scene graph and a scene object that the user can utilize as a high level API to add objects to the scene graph.

Fixes #8

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• Code follows the style guidelines of this project
• Code has been self-reviewed
• [will do for full master PR] Code has been commented, particularly in hard-to-understand areas
• Needed documentation changes have been made
• Code generates no new warnings
• Tests have been added that prove the code is effective or that the feature works
• New and existing unit tests and integration tests pass locally and the new code
• Any dependent changes have been merged and published in downstream modules