Since GOA is still using WebKit1, we need to set the environment
variable ourself. We can stop setting it once we port to WebKit2
because the network process will handle it for us.
https://bugzilla.gnome.org/show_bug.cgi?id=739960
This promotes better encapsulation and allows us to move
application logic out of main() and rename the confusingly
named control-center.c to main.c
https://bugzilla.gnome.org/show_bug.cgi?id=692174
