Added initial Comment model

refs https://github.com/TryGhost/Team/issues/1664

core/server/models/comment.js

@@ -0,0 +1,43 @@
+const ghostBookshelf = require('./base');
+
+const Comment = ghostBookshelf.Model.extend({
+    tableName: 'comments',
+
+    defaults: function defaults() {
+        return {
+            status: 'published'
+        };
+    },
+
+    post() {
+        return this.belongsTo('Post', 'post_id');
+    },
+
+    member() {
+        return this.belongsTo('Member', 'member_id');
+    },
+
+    parent() {
+        return this.belongsTo('Comment', 'parent_id');
+    },
+
+    emitChange: function emitChange(event, options) {
+        const eventToTrigger = 'comment' + '.' + event;
+        ghostBookshelf.Model.prototype.emitChange.bind(this)(this, eventToTrigger, options);
+    },
+
+    onCreated: function onCreated(model, options) {
+        ghostBookshelf.Model.prototype.onCreated.apply(this, arguments);
+
+        model.emitChange('added', options);
+    }
+});
+
+const Comments = ghostBookshelf.Collection.extend({
+    model: Comment
+});
+
+module.exports = {
+    Comment: ghostBookshelf.model('Comment', Comment),
+    Comments: ghostBookshelf.collection('Comments', Comments)
+};