Allow external file picker

This change to the shortcut feature launches a file picker chooser when the "Find command" button is pressed -- one of the choices is the internal FSNavigator. I should have done it this way initially. FSNavigator is ugly but it is functional, and the device might not have any other application which is registered as a file picker, so I left it in. 

The code uses a shared preferences boolean to determine if the internal file picker should be used or if the request should be passed on to the system: 

<CODE>
                    if(SP.getBoolean("useInternalScriptFinder", false))
</code>

This is done so that programmers wishing to add the option to the preferences activity of their personal fork can do so by only modifying the preferences activity. 

Frank