evas vg: enable visibility true by default.

evas vg: enable visibility true by default.

So far, vg shapes had been rendered regardless of its visibility.

Recently, I pushed a patch - fa1420965dd264fc8836d133a3215b94e423b8bf
not to render nodes which is invisible. This occurred a side effect
because previous vg implementations didn't take care of nodes visiblity.
It means, though vg users didn't make nodes visible but nodes were
rendered in unintended way.

This is a sort of compatibility problem but I can't let vg users
to change their nodes visible by calling visible set api explicity.
Instead, I'm gonna change the nodes visibility default value to true
so that skiping invisible nodes and compatibility issue as well.

Change-Id: If95f369ee984516ad515cfe0c01866c7c65dd852