Allow sending signals to GROUP sub-parts.

Allow sending signals to GROUP sub-parts.

Today signals emitted inside GROUP sub-parts are delivered to parent
group as "part-name:original-source". This is good and allow edje
groups to be reused. But no counter part to send events to inside
sub-groups existed.

This patch allows one to send a signal "signal" to inside a part
"part" that is of type GROUP by prepending signal emission with part name:

    emission: "part:signal"
    source: "source"

this is the same as:

   o = edje_object_part_swallow_get(ed);
   edje_object_signal_emit(o, "signal", "source");

but can be done all in themes, no need to go to application c/c++/python.

Based on patch by Pieter, see mail list.

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/edje@40489 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33