Just a couple quick feedback items. I had a little trouble finding that Add/Remove Icons' link and after i selected AWS in the preferences i couldn't figure out how to make it go away and get back to the palette. Moving that to the navbar on the left with a gallery type icon might work.
One other suggestion would be to lock the aspect ratio of any kind of stencil that has a product logo in it.
Again these are just minor nitpicks, fantastic work!
Clicking on the 'user preferences & settings' icon (on the left-hand bar) will take you to the same location. But yes, I agree that the UX could definitely be improved here.