skel: add gimp config:

- single window mode
 - show dockable toolbars

config/includes.chroot/etc/skel/.gimp-2.8/sessionrc

@@ -0,0 +1,11 @@
+# GIMP sessionrc
+# 
+# This file takes session-specific info (that is info, you want to keep
+# between two GIMP sessions).  You are not supposed to edit it manually, but
+# of course you can do.  The sessionrc will be entirely rewritten every time
+# you quit GIMP.  If this file isn't found, defaults are used.
+
+(hide-docks no)
+(single-window-mode yes)
+
+# end of sessionrc