Creates a skinnedbutton with the given
string as caption. The skinparam table content is used as arguments
for the SkinnedImage constructor. The SkinnedImage should have 8 states:
set a custom l2dnode for own purpose. The previously set custom l2dnode is
deleted. The new customl2dnode ist also deleted if the button is deleted.
The new customl2dnode is returned by this function. If no l2dnode is given,
the old customl2dnode is deleted.