appDisplay: Reorganize AppDisplay actor hierarchy
Right now, the actor hierarchy is such that the scroll view does not contain the actual grid. It looks as follows:
StScrollView
↓
StBoxLayout
↓
ShellStack
↓ ↓
PaginatedIconGrid StWidget
This hierarchy can be slightly reorganized by changing it to be as follows:
ShellStack
↓ ↓
StScrollView StWidget
↓
StBoxLayout
↓
PaginatedIconGrid
This will simplify future work where the PaginatedIconGrid will be an implementation of StScrollable, in which case we'll be able to simply remove the StBoxLayout from there.
Edited by Georges Basile Stavracas Neto