Add light/dark theme toggle option

[spcanelon]

References (least to most complicated):

• csv,conf,v6 - May 4-5 2021 - Online for gray theme toggle
  • html and JavaScript
  • css
• panr/hugo-theme-hello-friend: Pretty basic theme for Hugo that covers all of the essentials. All you have to do is start typing!
  • html layout
  • JavaScript
  • css
• Hugo Academic:
  • html layout
  • Toggle JavaScript
  • Theming JavaScript