ext/pango/gsttextoverlay.c: Revert API/ABI break from March 1. Keep 'halign' and...

ext/pango/gsttextoverlay.c: Revert API/ABI break from March 1. Keep 'halign' and 'valign' as string type properties, ...

Original commit message from CVS:
* ext/pango/gsttextoverlay.c: (gst_text_overlay_class_init),
(gst_text_overlay_init), (gst_text_overlay_set_property),
(gst_text_overlay_get_property):
Revert API/ABI break from March 1. Keep 'halign' and 'valign'
as string type properties, but mark them deprecated. Add
'halignment' and 'valignment' properties that use enums
instead of strings.