Create a theme for the React frontend

[hydrielax]

We need to create a MUI theme for the React frontend of Nantral Platform (for the v2 which will be developped).

Steps

• [x] 1. Create the light theme
• [x] 2. Create the dark theme
• [x] 3. Add a theme swicth in the user menu, with 3 options: Auto (follows system theme), Dark and Light. Auto is default

Infos

• Generator of the theme: https://bareynol.github.io/mui-theme-creator/
• The color of the graphism chart:
  • #b6b7b7
  • #e0e0df
  • Gradient from #b6b7b7 to #e0e0df
  • #dc3545
  • #ffc107
  • #0d6efd
• Exemples of icons using this colors:
  • repo directory: https://github.com/nantral-platform/nantralPlatform/tree/master/backend/static/img/icons/scalable
  • facebook picture: https://www.facebook.com/photo/?fbid=190244660042979
• How to implements a theme: https://mui.com/material-ui/customization/theming/

[rravelli]

Fix dark theme for join button. Font turn black when selected.

[ManonC12]

Fix the difference of color between accordions and buttons in the dark theme.