Notification: Fix application name used in internal notify#

GetCallingAssembly() returns the notify-sharp assembly when you use
constructors which chain upon the base constructor of Notification.
That means some notification systems, like the one in GNOME shell 3.2,
would then display "notify-sharp".

To work around this, use GetEntryAssembly() instead to get the
application's assembly name. Fixes bgo#656533.

Signed-off-by: Bertrand Lorentz <bertrand.lorentz@gmail.com>