Add office:font-face-decls to presentation template

Otherwise odf_new_document('presentation').insert_style(
   odf_create_style(...)) fails for font styles.

Full failing test snippet:
odf_new_document('presentation').insert_style(
   odf_create_style(
                'font-face',
                name=u'Arial',
                font_name=u'Arial',
                font_family=u'Arial',
                font_family_generic=u'modern',
                font_pitch=u'fixed'),
            automatic=True)