plasmawindowed didn't set any minimum size to its window,
so it could be resized unusably small.
it tried to find its attached Layout, but the attached property
object wasn't created.
now set the minimum size by the following heiristics:
- if there is a switchsize, set it to switch to full representation
- then take the full representation minimum size if available and bigger then switch size
- otherwise, set it as SizeEnormous icon size
- in any case, don't let the window be less than that