Reduce unnecessary renders and use js divIcon templates

[TurtIeSocks]

• Reorganizes the mui theme to be a little more performant and easier to read, maybe?
• Moves global styles into its own, static component to cut down on unnecessary style sheet creation
• Fixes a flash upon load when using light mode
• Uses user preference for dark mode as the initial setting for dark mode
• Turns all lazy react divIcons into javascript templates, which performs about 10x
• Also does a localStorage check at startup