Some websites are using images of O(10kB) when not )O(100kB) for their
favicons. As miniflux only displays them with a 16x16 resolution, let's do our
best to resize them before storing them in the database. This should make
miniflux consume less bandwidth when serving pages, for the joy of mobile users
on a small data plan.
Of course, images that already are 16x16 aren't resized.
