Examples: Added standard launch file for OSX

Add a simple launch configuration for OSX. The camera can be selected by
changing the default="0" to the appropriate integer.

Afterwards, the video can be accessed by 
```
roslaunch gscam osx.launch 
```
and visualized with
```
rosrun rqt_image_view rqt_image_view
```
![screen shot 2014-05-20 at 10 24 03 pm](https://cloud.githubusercontent.com/assets/1118185/3035507/0ba10c88-e08f-11e3-92ab-564e3d2e6da4.png)

Fixes #14.