Experimental colors

[barollet]

Overview: What does this pull request change?

It removes color attributs from Mobject and OpenGLMobject and fully delegates it to the vectorized child.
Some code is factored into a new ManimColorArray class in the color core file. This class handles creating and updating arrays of colors and opacity regardless of wether a single argument, list or no argument are given for opacity and color. Color and opacity attributes are now instances of this class instead of two separate attributes.
The get_colors and get_opacities variants are modified to access this new attribute so the change is not breaking if we keep using the getters and not direct attribute access.

Motivation and Explanation: Why and how do your changes improve the library?

Mobject is a baseclass where instances are not supposed to be displayed so color attributes do not belong here.

Links to added or changed documentation pages

Further Information and Comments

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested