Tweak scoring rules

Adjust them towards larger images, now minimum width not downscored into
oblivion is bumped from 100 to 120 which is the minimum thumb size in
preferences. And the upper limit for maximum score is up from 300 to
400, since the maximum in prefs has grown recently.

Ping vaguely related bug: 72276

Change-Id: Ia81310964d5446833cca11aef1ce9a82f44da991