Add icon option to notify-send and kdialog

Hi, 
this pull-request allow a user to add an `icon` option to change the icon of the notification.
I have changed `notify-send` and `kdialog`.
I have tested those changes in `pry` on a Debian distribution.
I have also tested in `pry` in a Mountain Lion environment.

I guess it will work as it was for the others methods.

Bye.