WIP: Resolve "Follow-up from Resolve Improve GUI esthetic"

What does this MR do?

This MR adds new documentation for icons.

I think we need a better color palette, people who read this MR would be very nice to help me find one.

Associated Issues/Merge Requests

• Issues

  • Closes #25 (closed)
  • Closes https://git.ircad.fr/Sight/sight/issues/222

• Merge requests

  • https://git.ircad.fr/Sight/sight/merge_requests/112