Bring color of OS X app icon in line with others

I tinkered with the OS X app icon a little today since I felt like the red that's currently used isn't quite as saturated as the red that's used in the Toggl icon on the web and the mobile apps.  I started with the on.pdf file in test2.project and tried to keep things as close as possible to the current icon.  It's not as good as working from the original file, but I think it turned out okay.

Other than the color change, the only other notable visual difference is with the icon's drop shadow.  I looked around at the shadows on other OS X icons and it seems like most icons have the light source coming down from above the icon (whereas it's coming at an angle from the top left in the current icon), so I set the drop shadow to 90 degrees and tried to make it similar to most apps.  [I also re-did the inactive icon in the same fashion so it's in line with the revised icon.]

Past that, I exported the icon at 1024px x 1024px and created @2x files so it should look nice on Retina displays.

I've attached an image showing the changes (with the current icon on the left and the revised version on the right), so let me know what you think.  If you like the changes then feel free to just merge the pull request (remember to relaunch the Dock (with `killall Dock`) to see the change), but if anything could be better just let me know and I can go back and make some changes.

![toggl_osx_app_icon_changes](https://cloud.githubusercontent.com/assets/1584702/2624493/38590ff0-bd44-11e3-80fd-67531ee67f8f.png)