theme: Decrease padding on folder view popup

If a folder view is scrolled, its scrollbar ends up too close to the
content (even partially overlapping it) with the current padding.
Making it much smaller fixes the issue without affecting the content
position - the removed padding will just move to IconGrid's dynamic
padding.

https://bugzilla.gnome.org/show_bug.cgi?id=707662
appDisplay: Increase fade offset in FolderView

Just as we do in AllView, we set the offset of FolderViews' fade
effect so that no icon is faded when a full page is visible.
This works fine in AllView, however in the FolderView case where
the popup's offsets eat away from the available fade height, the
effect ends up being barely noticeable at all.
While it is not ideal to apply the fade to the edge of a "full page",
it looks less ugly than the current state, so pick the lesser evil ...

https://bugzilla.gnome.org/show_bug.cgi?id=707662