Popover: Remove the need for `relative` prop

[chrisolsen]

Info

People don't understand the need or usage of the relative prop used in the Dropdown and Datepicker component, which is then passed to the Popover component.

Ideally we wouldn't need to set the relative property, and it should work in all scenarios, the position is always properly calculated.

The relative property is currently needed if the Dropdown or Datepicker component is placed inside a positioned parent container.