Add Mongoose wrapper class ChatData

mongoose.js

+class ChatData {
+  constructor () {
+    this.mongoose = require('mongoose')
+    this.mongoose.connect('mongodb://localhost/wbd3_chat')
+
+    this.chatSchema = new this.mongoose.Schema({
+      participant_ids: [Number],
+      chats: [{
+        owner_id: Number,
+        content: String
+      }]
+    })
+    this.ChatModel = this.mongoose.model('Chat', this.chatSchema)
+  }
+}