new icon for rqt

The flat, square background did not look good on OS X. It is still blurry, but there seems to be no way to get hidpi images in the dock without using a .app bundle and an info.plist file.

I created it with omnigraffle to get the drop shadows and stuff, so I saved the graffle file into the repo as well. I exported a svg copy of it, but it seems to use svg stuff that Qt doesn't support, plus it doesn't look any better. So I saved out a 1024x1024 png, which looks fine and has the drop shadow. I haven't seen what this looks like on Linux.

This is the png:

![rqt](https://f.cloud.github.com/assets/100427/1294990/3676a9ca-309c-11e3-9c06-34986dcf1f4e.png)

This is what it looks like in my dock:

![screen shot 2013-10-08 at 9 28 29 pm](https://f.cloud.github.com/assets/100427/1294993/3d525622-309c-11e3-865e-2e66174441a3.png)

This is what the old one looked like:

![screen shot 2013-10-08 at 9 36 39 pm](https://f.cloud.github.com/assets/100427/1294998/840585d0-309c-11e3-8a09-6a6f95bb5e1e.png)

I tried to make the new one using svg directly, but I couldn't get the rounded edges to behave. In the end it is sort of subjective, but I personally think this looks nicer, thoughts?