gs-application: add a local file to define personal customizations.
CSS files of GNOME Software are built-in, so there is no way to put your
own customizations to create an specific App Store. This patch adds a
local css file at /usr/share/gnome-software/
to enable non-default CSS
customizations. Important: This method is sensible by theme changes.
Signed-off-by: Julio Faracco jfaracco@br.ibm.com