Enhancement/color

[iozbeyli]

Try on http://134.209.254.13:8888/

Checklist

• [x] I added multiple screenshots/screencasts of my UI changes

Motivation and Context

• Adding colors improves the information that is transpired through uml diagrams
• Colors can be used to show related elements between two diagrams (useful for plagiarism in Artemis for example)

Description

• Adds fill, stroke and text color to elements.
• Users can choose it from a predetermined list of colors to keep the overall structure simple

Steps for Testing

1. Create each diagram and each elements and connect them to each other
2. Color each element

Screenshots

https://user-images.githubusercontent.com/16825065/118381922-43405480-b5f0-11eb-8eb2-e40a65a34dd2.mp4

[iozbeyli]

I have some change requests / questions:

1. can you display the color options below the model elements (in case something is selected) so that the elements are always visible?

2. The terms stroke sounds wrong. Can you use `line color`? And for the others please use `fill color` and `text color`.

3. Did you add German translations as well?

4. And how would this work in Artemis? (would this be activated by default? what happens to the colors used in the assessments?) I don't think this functionality is needed in Artemis, so developers who use the library should be able to disable coloring options.

5. Did you write tests? If yes, please add the test coverage to the PR description

1. Yes, I can do that but it would make it hard to use. Listing elements on the side when something is selected has no use that I can think of. Listing useful information about the selected elements is more beneficial but of course I can do it if you want.
2. and 3. I can change the names and add translations I missed that part.
3. Any of the colors that was used before overwrites the user set colors. I can add the disable option or even add an enable option if you prefer that one.
4. I will add the tests.

Additionally, should I add a legend for colors, I see that it is commonly used in presentations?

[krusche]

1. I would still prefer this, because users might be confused why the model elements suddenly disappear. It's very common that a model element is selected and users might not find the model elements to drag in any more then. Also, you can still drag and drop elements even if something is selected. The selection will just disappear then.
2. Add an enable option. I think colors are problematic in this context.