Added StartupWMClass=processing-app-Base to Linux .desktop file.

This should group all open Arduino IDE windows together under one icon (i.e. Ubuntu Unity launcher)

Author: fiechr

build/linux/dist/desktop.template

@@ -9,3 +9,4 @@ Terminal=false
 Categories=Development;IDE;Electronics;
 MimeType=text/x-arduino
 Keywords=embedded electronics;electronics;avr;microcontroller;
+StartupWMClass=processing-app-Base