The icon-only button must still have a label for screen readers, but that should not be shown visually to the user.

Use bootstrap class, also already used in query builder: #74

• should be added centrally somewhere, so it is reusable in all wikit components

Adding aria labels seems to be the standard approach.

<Button aria-label="label goes here">
    <Icon ... />
</Button>

See docs: https://www.w3.org/TR/WCAG20-TECHS/ARIA14.html