config: allow font/foreground attributes on modules too

Previously we allowed it on the bar, and on all particles. Now we also
allow it on all modules.

This allows us to specify a "default" font/foreground on a per-module
basis, having it applied to all the modules particles.

modules/backlight.c

@@ -231,7 +231,7 @@ verify_conf(keychain_t *chain, const struct yml_node *node)
         {"name", true, &conf_verify_string},
         {"content", true, &conf_verify_particle},
         {"anchors", false, NULL},
-        {NULL, false, NULL}
+        MODULE_COMMON_ATTRS,
     };
 
     return conf_verify_dict(chain, node, attrs);