Handle image loading rejections

Displays the rejection error message when loading something fails, so that the
user knows what's going on and can send meaningful error reports.

Needs non-crappy design.

Change-Id: I7d2914d89549b598bd1070ed40c6f1c9d45b55f0
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/271