add helper ecore_evas_object_associate.

add helper ecore_evas_object_associate.

We usually want to create an Ecore_Evas and attach an object to it, be
it the background, your smart object that will manage the scene (ie:
edje) and this is replicated everywhere. Not anymore!

ecore_evas_new() and ecore_evas_object_associate() will behave much
like regular toolkits "window-new()" and "window-main-child-add()",
actually it was based on elm_win.c and hopefully we can remove that,
or most of that code and replace with this helper.

I'll add an Evas smart object to handle stacks of objects, that is, it
will be a clipped smart object that on resize it will resize every
child to the same size. This means we can associate this stack object
and add a background and then your stuff on top of it.

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/ecore@37010 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33