Fontconfig: expand options and allow overriding upstream
fontconfig: include upstream configuration by default again
fontconfig: remove extra options
infinality: add NixOS module for user settings

There are many Infinality settings which are intended to be
user-configurable, but the Infinality settings resided in the read-only
Nix store. This module allows those options to be configured and
documents them. Some enviroment variables must also be set according to
the desired style to activate the Infinality FreeType patches. The many
style presets that ship with Infinality are exposed by this module.
fontconfig: don't load global config from /etc/fonts/conf.d
fontconfig: reorganize NixOS options
fontconfig: use upstream Infinality settings by default
infinality: don't load upstream config when disabled
Add SourceSansPro-1.050
Add SourceSerifPro-1.014