Clarify meaning of visuals to the users

[theFeu]

@losten-git was approached with a request for more clarity about the visuals in lists.

^ said visuals

This was about adding explanations about the colours of our default theme, and maybe also use of icons to our concept documentation - as discussed with @lippserd

Another thing that came up while discussing this was, that we could add titles to the visuals that just describe their state, so they explain what they mean when hovered.

[idandr]

Extending the documentation would be great. I was looking for information about the meaning of the flash icon in the visual and landed here.

Edit: Found the answer in #819 - flash means flapping.