添加站内消息，修复讨论节点丢失的问题

hydro/lib/nav.js

@@ -0,0 +1,18 @@
+const permission = require('../permission');
+
+global.Hydro.ui.nav = [];
+
+const Item = (path, name, prefix, perm) => {
+    global.Hydro.ui.nav.push({
+        path, name, prefix, perm,
+    });
+};
+
+Item('/', 'domain_main', 'domain_main');
+Item('/p', 'problem_main', 'problem', permission.PERM_VIEW_PROBLEM);
+Item('/t', 'training_main', 'training', permission.PERM_VIEW_TRAINING);
+Item('/discuss', 'discussion_main', 'discussion', permission.PERM_VIEW_DISCUSSION);
+Item('/c', 'contest_main', 'contest', permission.PERM_VIEW_CONTEST);
+Item('/manage', 'domain_manage', 'domain_manage', permission.PERM_MANAGE);
+
+global.Hydro.lib.nav = module.exports = Item;