evas/elm: Remove group_show and group_hide

evas/elm: Remove group_show and group_hide

These should be just overrides of Efl.Gfx.visible.set. Many
widgets were handling smart show() and hide() manually, which
means this patch is quite large.

Hopefully this doesn't break anything, obviously. But here are
some widgets known to be problematic, as the old code flow was
really strange (sometimes not calling the efl_super function):
 - window
 - notify