[CINNAMON SETTINGS] Added flickr support for slideshow

Added flickr icon and changed the makefile.am
Destroy dialogs, don't just hide them unless you've got a really good reason to.

A dialog should go:

<new dialog>
<prep dialog>
dialog.show_all()
dialog.run()
<handle response id's, destroy afterwards.>

Right now the 'Close' button does nothing (and I think it should be 'Cancel', not Close)