Update countdown for Leap 15.5 poo#114022

[lkocman]

• add graphics from openSUSE/artwork prototype folder it fits the best imho
• use June 7th as GA date

[lkocman]

I do like the "Leap 15.5" + available in the other div better than original Leap wording.

[lkocman]

So MicroOS is basically misusing our release counter space as of now. We can perhaps revert this commit after GA. Suggesting 20th of June.

[ddemaio]

@lkocman There is no countdown showing