KCardGrid: Should align items whether selectable or not if any are selectable

[nucleogenesis]

Expected behavior

When KCardGrid has a mix of selectable and non-selectable items, the non-selectable items do not have the space where their checkbox would be left empty - but instead, the card extends the full width.

See this code in Kolibri which was used to provide this padding for this particular case.

Actual behavior

If any items are selectable in a KCardGrid, then all of them should be aligned and the same width.