[GUI.Qt] Refactor a bit the way runSofa is implementing the scenegraph colors

[damienmarchal]

The current implementation has flawns among which:

• lack of factorization between node & object rendering in the scenegraph view;
• the use of hardcoded color scheme in simulation:Colors

Here is a small attempt to change some of these aspects without the ambition to fix everything.
Additionally, I would like to be able to add more colors/rendering scheme for objects that are not part of the base framework and wonder if we need to implement an extension mechanism so that object defines in plugins (eg: sofapython3::BasePrefab) can propose their own icon in the scene graph.

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By submitting this pull request, I acknowledge that
I have read, understand, and agree SOFA Developer Certificate of Origin (DCO).

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Reviewers will merge this pull-request only if

• it builds with SUCCESS for all platforms on the CI.
• it does not generate new warnings.
• it does not generate new unit test failures.
• it does not generate new scene test failures.
• it does not break API compatibility.
• it is more than 1 week old (or has fast-merge label).

[hugtalbot]

PR just got updated.
Several points are below this PR:

• define a new design for managing colors by component
• should the color API allow for new colors
• Should Prefab be refactored in Sofa.Core ?

→ wip : PR should keep only the 2-line change

[damienmarchal]

@hugtalbot I don't understand what you are refering by 2-line change :)