Custom action icons for tray icon menu

I have been working on some custom icons for the actions in udiskie's tray icon menu. The design of the icon set is geared to the [Tango Icon Theme Guidelines](http://tango.freedesktop.org/Tango_Icon_Theme_Guidelines). The icons have to be installed into the default GTK icon theme `hicolor` in order to work. (Instructions for that have been placed in the readme file.)

PS: I think I would like to extend this work to the tray icon itself, which atm is a simple CD-ROM. Something more unique/characteristic would probably be nice. However, since this sort of acts as an avatar for udiskie itself, some input about what it could look like would be appreciated.