functions.sh: Allow generic TEMPLATE_FLAVOR_DIR that matches all flavors, or even no flavors

Use an asterisk in place of a '+flavor' to indicate a template directory to be applied
to all flavors, or no flavor at all.

    *:/home/user/qubes/qubes-src/some-repo/template-directory

functions.sh

@@ -209,6 +209,11 @@ templateDirs() {
         elif [ "${element:0:1}" == "+" -a "${element%:*}" == "+${template_flavor}" ]; then
             eval echo -e "${element#*:}"
             match=1
+        
+        # Generic template directory that matches all flavors, or even no flavors
+        elif [ "${element:0:1}" == "*" ]; then
+            eval echo -e "${element#*:}"
+            match=1
         fi
     done