Show error toast messages when there is no room for the item when icon is not...

Show error toast messages when there is no room for the item when icon is not to be added to folder.

* when user tries to add item to full hot seat from workspace.
* when user tries to add item to full home screen from workspace.
* refactored so that Workspace handles displaying error messages.

Bug: 15574422
Change-Id: Ibc98c7f45bc0c646dc4636660fba62be9db22ac0