set initial file icons based only on type

A small change that should fix #1431.

If you look at [the comment][1] above my change in `setQuickIconForObject:` (or if you just think about it), it should have been this way all along.

I wonder if it was in the past, because I remember `iconForFile:` was being called in both methods. I removed the call from `loadIconForObject:` at one point, but I've put it back with this commit.

[1]: https://github.com/skurfer/Quicksilver/pull/new/fileIcons#L0L139