[Paul2803k]

Some fixes to the UI system to bring it up to speed, especially in preparation for expansion.

• Colors. The color options went from seven to five, and each one now looks different. The warning yellow is easier to see.
• Buttons. Buttons keep the same border as their fill in every state. Outlined buttons fill in when you hover them.
• Sizes. Buttons, inputs and dropdowns share three sizes (small, medium, large) and line up when placed next to each other. The default is a bit more compact than before. Icons and loading spinners have a short, matching size list.
• Text. There are fewer text styles, and titles get smaller in a consistent order. Headings follow a proper order in the page structure.
• Dark mode. Loading spinners now follow dark mode.
• Cleanup. Shared base styles replace a lot of repeated styling, and unused code is removed.
• Component names. Settings that do the same thing have the same name in every component.
• Smaller fixes. The file upload area looks disabled when it is disabled and is less tall. The export button no longer stretches to full width by default.
• Pages no longer shift sideways when a scrollbar appears.