FAB component implementation for theme selection

[BSoDium]

The transition from desktop to mobile mode currently isn't fully lossless interaction-wise. The theme switching button, available in both desktop and tablet mode disappears.

The easiest and cleanest solution is implementing an equivalent of Material Design's FAB:

The following basic features are required:

• Basic theming compatibility with the MUI Joy design system
• Functional display of the current state, as well as circling between Light, Dark and System modes
• Sizing options