#1067: Overwrite MoM classnames instead of adding to the list

[sarahfossheim]

Issue

Styling was being added to the month over month components by adding to the classList:

changeSlot.classList.add(styling.color, styling.direction)

or:

changeSlot.classList.add('monthchange', styling.color, styling.direction)

As a result, the icons were added twice when switching between mobile and desktop (which doesn't reload the page or clear out the existing components).

Fix

Instead of adding to the classList, the className now gets overwritten:

changeSlot.className = `month change ${styling.color} ${styling.direction}`.

[tunetheweb]

I think you broke this in #1068 as 0's weren't showing so fixed it here.