Two panel home empty page removing logic change

- Don't remove a single page if it's empty, only if both pages are empty.
- Add back empty pages after they were removed while the phone
  was on single panel home.
- On two panel home don't add new workspace items onto the second screen

Test: manual
Bug: 196376162
Change-Id: I4c54ffa3b359a236deb3ab67adb54111e77ec896