Generate share/glib-2.0/schemas/gschemas.compiled in system-path.

This is required to create a gschemas.compiled file with content
from all gschemas. Otherwise, gschemas.compiled will be taken
from a random package, and gsettings programs will not find what
they are looking for. I had to add this to get NetworkManager-applet
to work. You'll also have to add share/glib-2.0 to the pathsToLink
list.

Generating this in the activation script (along with gtk icons
etc), is not the nicest solution. But I have no real idea on
how to modularise it.