[key event focus handling] (1)hotseat <-> icon now symmetric, (2)support DEL keycode

TL;DR; (1) Key event navigation from and to the hotseat and icons in the workspace
is now symmetric. Since there is one more icon in the hotseat, only left
N-1 icon navigation was symmetric.

(2) KeyEvent.KEYCODE_DEL and KeyEvent.KEYCODE_FORWARD_DEL can now delete icons
from the workspace. The focus move to the previous icon where the focus
traveled from.

Also contains minor styling and indexing issues.

Bug: 15408321
Bug: 19381790

Change-Id: I16cbcb2693e92eebb830997d01c0bf674073dd51

src/com/android/launcher3/Workspace.java

@@ -4231,6 +4231,9 @@ public class Workspace extends SmoothPagedView
         mDragInfo = null;
     }
 
+    /**
+     * For opposite operation. See {@link #addInScreen}.
+     */
     public void removeWorkspaceItem(View v) {
         CellLayout parentCell = getParentCellLayoutForView(v);
         if (parentCell != null) {