appDisplay: Paginate AllView

Organize applications in AllView by pages using the new PaginatedIconGrid
added previously. Pagination is generally a better pattern for collections
than scrolling, as it better suits spacial memory.
Hook into AppDisplay's allocation function to communicate the available
size to the different views before child allocations - this is only
required by the paginated view (as pages must be computed before
calling get_preferred_height/get_preferred_width), but doing it for
all views will guarantee that their dynamic spacing calculation is
based on the same values.

https://bugzilla.gnome.org/show_bug.cgi?id=706081