Prepare bpmn-js-color-picker to be included in camunda modeling

[smbea]

What should we do?

Do some refining and clean up:

To-Do:

• (for now) Match UI to the one shown here: https://github.com/camunda/camunda-modeler-design/issues/101
• Generate color icons (via data-URL) based on defined colors (instead of defining it with CSS for each color) (Generate colors based on actual color values, not CSS classes #12)
• Allow colors to be configurable (and therefore customisable by users) (Add colors configuration #11)
• Integrate it into the multi-element context pad (Integrate with multi-element context pad #13)

Why should we do it?

Improve the color picker in order to include it in camunda-bpmn-js.
Allow color extensibility for bpmn-js users.

[CatalinaMoisuc]

@smbea do we already know exactly which version of camunda-bpmn-js will include this feature?

[smbea]

Since this hasn't been worked on yet, it won't be included in the next version (for the next Desktop Modeler release). But should be included after that. I'm guessing @barmac may work on this, since he's taking on the multi-element context pad actions

[christian-konrad]

As discussed, I decoupled it from the https://github.com/orgs/camunda/projects/9/views/11 epic.

[CatalinaMoisuc]

We gave priority to the append anything epic over this. Moved to backlog for now.

[nikku]

Color picker updated to bpmn-js@11 / modern popup menu:

[nikku]

Will be fixed via #14.