New component: Switch.

Switches can be used instead of regular radio buttons, to switch between two or more options. They are very customizable and use styles from other components such as buttons or panels.

The switches are CSS-only, and only show-up only modern browsers. Browsers without support for media queries get standard form elements.

The class names used are similar to the ones used by F4 classes for grids (`.switch`, `.switch-3`, `.switch-4`, `.switch-5`).