webapp: fix creation form

[tharvik]

see #690 for context

• webapp
  • redo form
    • split into more categories
    • make it nicer (no more loooong input field, grid layout on bigger screen)
    • greatly simplify fields implementation (no more type specific container, no dynamic form)
  • rework the internal layout of many pages to better separate concerns
    • avoid some forced sizing
    • have common cards-gap CSS class instead of inconsistent gap
  • nicer data example layout
  • testing
    • fix unconsistent temporary server URL
    • spin test server on another port to avoid having to kill dev-server to launch tests
• discojs
  • mv Task.TrainingInformation.dataType to Task.dataType
    • allows Task.DisplayInformation to be type dependant
  • redo most of Task.DisplayInformation