[Telepathy] Exclude Empathy from Alt-Tab candidates in Gnome 3

[Roy Hyunjin Han]

Thanks for your work on Empathy.  Is it possible to exclude Empathy
from the list of programs that appear when I press Alt-Tab?  I would
prefer Empathy to be strictly a Gnome panel applet similar to the
behavior of the gnome-alarm-clock.

Having Empathy in the list of Alt-Tab candidates gets in the way when
I want to switch between programs quickly.

Thanks,
RHH