theme: Use gnome-shell-sass as a submodule

The sass sources now live in a project in GNOME, so they can
be used in multiple projects like gnome-shell-extensions.
Because of that, add gnome-shell-sass as a submodule and import the sass
sources from it.

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "data/gnome-shell-sass"]
+	path = data/gnome-shell-sass
+	url = https://git.gnome.org/browse/gnome-shell-sass/

autogen.sh

@@ -12,6 +12,14 @@ test -f $srcdir/configure.ac || {
     exit 1
 }
 
+# Fetch submodules if needed
+if test ! -f data/gnome-shell-sass/COPYING;
+then
+  echo "+ Setting up submodules"
+  git submodule init
+fi
+git submodule update
+
 which gnome-autogen.sh || {
     echo "You need to install gnome-common from GNOME Git (or from"
     echo "your OS vendor's package manager)."

data/HACKING

@@ -0,0 +1,6 @@
+To generate the css files, from the project directory:
+
+sass --sourcemap=none --update .
+
+To update the gnome-shell-sass submodule to latest upstream commit:
+git submodule update --rebase

data/gnome-classic.scss

@@ -1,9 +1,9 @@
 /* Use the gnome-shell theme, but with light colors */
 $variant: 'light';
 
-@import "../../gnome-shell/data/theme/_colors"; //use gtk colors
-@import "../../gnome-shell/data/theme/_drawing";
-@import "../../gnome-shell/data/theme/_common";
+@import "gnome-shell-sass/_colors"; //use gtk colors
+@import "gnome-shell-sass/_drawing";
+@import "gnome-shell-sass/_common";
 
 /* Overrides */