Fix apps row align and update to new layout spec

1. Fix align bug when some item show exit icon.
2. Make items can be placed in the row center and alocated average
   size of the row when item number not enough to scroll.

Fix: 123047781
Test: manual
Test: atest DocumentsUITests
Change-Id: Iea129751b8423f026f107fdee19c42ae6e76feb3