Force all images to have a height, but remove it when layout is complete

See: https://github.com/GigaOM/gigaom/issues/5777

This was logic that was in this plugin before but was stripped out when it screwed with our CSS.  The fix is to add it back in (in a better location) and remove the manually set heights once layout has completed.
we are cool with the end result being all images have a height of `auto`?