Add configurable option to toggle file visibility on Application open

[geerlingguy]

See, for instance: http://code.google.com/p/hide-unhide/

Need to use a preference pane, allow user to set the preference, and then check for that preference in the application's startup logic.

We should create a separate class that has a function that checks the finder's current visibility.
And also we should have a function that switches the visibility and quits finder...

Can't have it quit the application automatically, because in that case, the preference would never be able to be un-set.