Grid change polish bugs.

- Folder icons were too small in landscape.
- Folders can now be 16dp away from the edge
  (used to be 64dp which resulted in super small folders)
- Decrease page spacing back to 8dp
- Decrease PreviewBackground accept scale factor since
  hotseat is now generally smaller.

Bug: 37014334
Bug: 37015359
Change-Id: Icbb53d34136bfdb93796d48f7379da6b9e214345