elm_panel: set hidden property when panel is close/open

elm_panel: set hidden property when panel is close/open

Summary:
elm_panel has a property named hidden which stores open/close status.
This is updated when:
  1.bring_in animation is done(anim_stop_cb).
  2.mouse_up on panel.
  3.API is called. (elm_panel_toggle, elm_panel_hidden_set)
In case 3, API changes hidden, and starts bring_in animation which will call anim_stop_cb() which will update hidden again.
If bring_in animation is canceled (eg: sizing_eval), anim_stop_cb will be called and calculate hidden status
which will not guarantee updated hidden state by APIs.

Test Plan:
1.Call any APIs which will call elm_layout_sizing_eval(panel) right after calling elm_panel_toggle()/elm_panel_hidden_set().
2.Delete content of panel during "toggled" cb.

Reviewers: jpeg, eunue, cedric

Differential Revision: https://phab.enlightenment.org/D4704

@tizen_fix

Change-Id: I8e0a97910de8bbc0920dd0260e3b81bc1793827e
Signed-off-by: JEONGHYUN YUN <jh0506.yun@samsung.com>