elm_index: include horizontal index to omit calculation

elm_index: include horizontal index to omit calculation

Summary:
- when index is set to horizontal by elm_index_horizontal_set()
  there is no logic about omit calculation. However, when
  omit is enabled/disabled by elm_index_omit_enabled_set(),
  horizontal index is ignored by
  if (sd->orientation == EFL_ORIENT_HORIZONTAL) return;
- This can cause inconsistency when order of calling those APIs
  is changed. And also, that "horizontal index cannot be omitted" is not documented
  and does not make sense.
- This commit enables omit for horizontal index, but further
  change is needed because current logic of getting min_w for
  dummy edje object is not accurate when text is set.

Reviewers: cedric, jpeg, Hermet, conr2d

Reviewed By: conr2d

Subscribers: eunue, conr2d, cedric, jpeg

Differential Revision: https://phab.enlightenment.org/D4052

Signed-off-by: Cedric BAIL <cedric@osg.samsung.com>