Don't restore wildly wrong sized wallpapers

If the dimensions of the original are sufficiently different from the
device's preferred dimensions, just don't restore the image.  This
avoids bad letterboxing / clipping on e.g. phone <-> tablet data
migration.

The expansion/shrinkage ratios used here allow restores of saved
wallpaper images among HVGA devices, among WVGA variants, and
among tablets; but skip restoring wallpapers across those
categories (where severe clipping or letterboxing would occur).

Bug 3261863

Change-Id: I75e75d6401d18f1df10d75796ee04e21d2302cfa