edje: implement text_class override at object level
implement text_class override at object level, where you can change the text_class for single textblock object instead of override all objects that share same text class.
This imported from TIZEN
This also fix edje_textblock font/font_size parsing by adding condition
Reviewed-by: Cedric BAIL <email@example.com>
Differential Revision: https://phab.enlightenment.org/D10598