New HiDPI Downloads menu and CPT admin icons. A little more clean and WordPress-ish.

If you like the icons and you want matching ones optimized for the normal 1x size, let me know. Also, I have PSD's where I created the icons, if you want those, as well.

Here's a preview of what this change looks like on retina MacBook:

![preview](https://f.cloud.github.com/assets/1952287/758806/1af6d1fc-e759-11e2-9013-07cdedfb52e1.jpg)

Also note that this commit fixes the following bug, as well:

![screen shot 2013-07-07 at 2 57 39 pm](https://f.cloud.github.com/assets/1952287/758807/25b2652a-e759-11e2-8fff-2459d3959fa4.png)