Clarify difference between auk-panel--gray-100 and auk-panel--editing

[MikiDi]

auk-panel--gray-100 vs auk-panel--editing. Apart from 1 unit of difference for the R component, both result in the same colour value. Do both of these classes exist next to each other on purpose, or should one of both be deprecated? In case both should be kept, clarify when to use which by means of a comment.

[brenner-company]

@MikiDi I don't know if you can see the following file (https://github.com/mono-company/kaleidos-prototype-v3/blob/master/content/js/modules/editable-panels.js), but the class they use at Mono within the prototypes is auk-panel--gray-100. Seems more logical & reusable then auk-panel--editing.

Is the following OK for you? Replacing auk-panel--editing within Kaleidos codebase and, after that, removing the class from this package?