Order child pages (#21)

* save ordering pages

* move to another collection

* requested changes. Code improvements

* add margin

* unit tests

* fix

* requested changes

* recursive method: create menu tree

* update comments

* fix bug

* requested changes

* move const

* fix error message on catch

* add migration

* rewrite to splices

* move methods

* testing put above method

* linter fix

src/utils/database/pagesOrder.js

@@ -0,0 +1,34 @@
+const Datastore = require('nedb');
+const config = require('../../../config');
+
+const db = new Datastore({filename: `./${config.database}/pagesOrder.db`, autoload: true});
+
+/**
+ * Current DataStore preparation
+ * Add initial row for RootPage
+ */
+(async function() {
+  const parentIdOfRootPages = '0';
+  const cbk = (resolve, reject) => (err, doc) => {
+    if (err) {
+      reject(err);
+    }
+
+    resolve(doc);
+  };
+
+  const order = await new Promise((resolve, reject) => {
+    db.findOne({page: parentIdOfRootPages}, cbk(resolve, reject));
+  });
+
+  if (!order) {
+    const initialData = {
+      page: '0',
+      order: []
+    };
+    await db.insert(initialData);
+  }
+
+}());
+
+module.exports = db;