Merging SceneObjectNode and SceneObject

[Licini]

The relation between SceneObjectNode and SceneObject was too convoluted. This PR merge them into one by having SceneObject inherent from TreeNode. This simplifies a lot on operations to access parent/ children object or a tree that an object is attachted too. While the most-outer level user APIs stays untouched. This should also make it easier from creating a compas_model object.

from compas.scene import Scene
from compas.geometry import Box
from compas.geometry import Sphere
from compas.geometry import Cylinder
from compas.geometry import Frame
from compas.geometry import Sphere



box = Box.from_width_height_depth(1, 1, 1)
cylinder = Cylinder(1, 1, Frame.worldXY())
sphere = Sphere(1)

scene = Scene()
scene.clear()

obj = scene.add(box).add(cylinder).add(sphere)

scene.print_hierarchy()


print(obj.tree)

└── <TreeNode: ROOT>
    └── <GeometryObject: Box>
        └── <GeometryObject: Cylinder>
            └── <GeometryObject: Sphere>
<Tree with 4 nodes>

What type of change is this?

• [ ] Bug fix in a backwards-compatible manner.
• [ ] New feature in a backwards-compatible manner.
• [ ] Breaking change: bug fix or new feature that involve incompatible API changes.
• [x] Other (e.g. doc update, configuration, etc)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• [x] I added a line to the CHANGELOG.md file in the Unreleased section under the most fitting heading (e.g. Added, Changed, Removed).
• [x] I ran all tests on my computer and it's all green (i.e. invoke test).
• [x] I ran lint on my computer and there are no errors (i.e. invoke lint).
• [ ] I added new functions/classes and made them available on a second-level import, e.g. compas.datastructures.Mesh.
• [ ] I have added tests that prove my fix is effective or that my feature works.
• [x] I have added necessary documentation (if appropriate)