Process /etc/fonts/conf.d before upstream fonts/conf.d

Otherwise the user won't be able to override anything specified in
NixOS' /etc/fonts/conf.d, since ~/.config/fontconfig is included from
upstream fonts/conf.5/50-user.conf.
google-talk-plugin: Enable screen sharing
disnix: push to latest 0.3 development release
moderntimeline: Add extra source URL