Move display mode switch icon to sub header

Based on designer mock dock, grid/list mode switch icon should
place on sub header rather than tool bar.

Remove apps row item min height to avoid too many white space
when all items in apps row is provider.

Remove some unused import.

Fix: 123569812
Test: manual
Test: atest DocumentsUITests
Change-Id: I4777b638764dd4a52be6b65e7d8adbd1f60beffa
10 files changed