Icon upload bug when icon is updated

[cvan]

Aviary support for icons was added in pull request #114. There's a weird bug when uploading another icon to replace an existing icon:

1. Add an icon.
2. Crop and save.
3. Add another icon.
4. Things get weird. (Notice the editor is all messed up. I think the wrong src is getting passed or something.)

My JS is probably bad when I'm doing the previewing and launching the Aviary editor.

[yangshun]

Fixed in #143