[Bug 889272] Fix z-index of contrib tools.

The contributor tools and the showfor menu both had z-index of 10. I lowered all the showfor z-indexes by 5, which still keeps them above the content, but below the drop downs on the top.

Also, I noticed that the contrib tools and the showfor menu interacting didn't look good, because it was a white menu overlapping a white element with no border or shadow, so I added a shadow on the left, bottom, and right, and removed the hard border on the bottom.

r?