[Gengrid] Fix gengrid item position update bug, when item is reordered or deleted.

[Gengrid] Fix gengrid item position update bug, when item is reordered or deleted.

Summary:
When gengrid item is reordered or deleted, gengrid didn't update item's position.
         This Patch update item's position when item is placed. if middle of item deleted,
         every item after the deleted one, will re-postion on _item_place function, so they
         will be update there position well.

Test Plan:
modify test_gengrid grid_sel fuction to print there position. so when item selected,
           they print there position and it works fine both horizontal and vertical.

Reviewers: bluezery, seoz, raster

Reviewed By: raster

CC: Hermet, chinmaya061
Differential Revision: https://phab.enlightenment.org/D855