Debounce resizes

* create a resize-end event which fires 100ms after resize ends
  (or pauses)
* move slow resize callback (fetching new thumbnail from the server)
  to resize-end

Change-Id: I1c1217ea43ffade4cfaf0c03f24574d0ebfee080
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/898
Log image dimensions

Also add a sanity test to attribution logging which I forgot at the time.

Change-Id: I3010e57eb74a76fee4078c415182a033375ea890
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/898
Merge "Debounce resizes"
Merge "Log image dimensions"