Added a simple way to customize the sensor gadget background. If any of the files gadget_background.png, gadget_image.png, gadget_foreground.png, gadget_bar_background.png or gadget_bar_foreground.png is present in the working directory then these files are used instead of the built in files.

 <?xml version="1.0" encoding="utf-8"?>

 <configuration>

   <startup>

     <supportedRuntime version="v4.0" />

     <supportedRuntime version="v2.0.50727"/>

   </startup>

 </configuration>