In the past, the icon grid would update the number of pages
during the call to adaptToSize(). However, after the new grid
layout landed, the number of pages is updated by the time an
item is added or removed.
Instead of comparing the old and new number of pages in the
icon grid, compare the pages shown by the indicator, and the
grid pages.
appDisplay: Allow a slighly bigger area for drag overshoot
Now that we don't have the Frequent tab anymore, and subsequently
the buttons to switch tabs, the app grid fill all the way to the
bottom, leaving no room for drag overshoot.
Add a 20px (i.e. OVERSHOOT_THRESHOLD) area at the bottom of the
grid where dragging actually scrolls to the next page.
appDisplay: Factor out shared code into BaseAppView
The two BaseAppView subclasses now share a lot in terms of
widgetry: they both have a scroll view, pagination dots, swipe
management, etc.
Move this shared code into BaseAppView. Notice, however, that
BaseAppView only creates the widgetry, but it doesn't add them
to any specific layout. FolderView arranges the widgetry in a
vertical box, while AppDisplay arranges it in a ShellStack.
Add a new 'orientation' parameter to BaseAppView and use it
to determine the orientation of the pagination dots, the swipe
tracker direction, and the scroll event handling.
It is worth noticing that the scroll event is a bit more
sophisticated now: when the orientation is horizontal, it
handles all directions since mice wheels usually only generate
up/down events.
Make the folder dialog's app grid horizontal, and add
paginators to it as well. Add a new _createGrid() method
to BaseAppView that created an IconGrid.IconGrid by
default, and make FolderView override it to return the
new FolderGrid class.
When FolderIcon is destroyed, it destroyed the FolderView and, if
there's a folder dialog present, it destroys the dialog as well.
Turns out, the folder dialog adds the icon's FolderView to itself.
The view becomes part of the dialog's actor tree. When the dialog
is destroyed, it also tries to destroy the view - but the folder
view was already destroyed by FolderIcon!
Fix that by letting the dialog destroy the folder view if it exists,
otherwise destroy the folder view directly.
