#26089 Added "not found" error dialog when running in the deskop engine.

When apps are launched from the desktop engine, and the configured path for an app isn't working, the following message is being emitted:

![screen shot 2014-08-06 at 00 52 35](https://cloud.githubusercontent.com/assets/337710/3820650/db51e7b0-1cfb-11e4-8b64-117fc9e876db.png)

Clicking the button will launch a web browser and the close the dialog.

 
Icon should be the gray shotgun in a circle, same as the about dialog.
The blue is a little strong against the dark background.