widget: Remove part_text from EO
It should be implemented as a efl_part() API.
For now I've only done a quick hack, as the only overrides were:
- notify: already a Part implementation. Also it turns out the default theme does not even have any text part in the notify group.
- combobox: not a Part implementation, but also very badly defined wrt. parts in general. efl_part() is handled by the parent class (button) which makes it tricky to override just for one function.
With this patch I'm trying to keep the same behaviour as earlier (where
efl_part() is used for layouts and there is a special path for