Summary:
Fixes T2643. Show a loading state (currently just making the image transparent, but we could do something fancier) when an image is loading.
Fixes T2648. Cleans up the double draws we were previously doing.
Makes thumbnails react to mousedown in addition to click so they feel a little snappier. Make them stop reacting to control click, command click, etc.
Test Plan: Used `setTimeout()` to simulate a 1s image load delay, switched between images.
Reviewers: chad
Reviewed By: chad
CC: aran
Maniphest Tasks: T2643, T2648
Differential Revision: https://secure.phabricator.com/D5219
5a7d9fb522