elementary gengrid: fix for working item reorder mode correctly

elementary gengrid: fix for working item reorder mode correctly

Summary:
Change the item indexing to start 1 after reordering animation.
Change the logic of edge checking to get the row or col correctly.

Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>
Test Plan:
elementary_test -to gengrid2
append 6 items
enable the reorder mode
check reordering is working properly (4 to 1)

@fix

Reviewers: singh.amitesh, cedric

Subscribers: jehun.lim, jpeg

Differential Revision: https://phab.enlightenment.org/D4676