Add include parameter for posts API

closes #2609
- added include parameter to api.posts.*
- changed toJSON to omit objects that are not included
- added include parameter to admin
- added include parameter to frontend.js
- updated tests
- removed duplicate code from posts model

**Known Issue:** It is not possible to attach a tag using an ID.

ghost/admin/models/post.js

@@ -49,6 +49,7 @@
             if (method === 'create' || method === 'update') {
                 options.data = JSON.stringify({posts: [this.attributes]});
                 options.contentType = 'application/json';
+                options.url = model.url() + '?include=tags';
             }
 
             return Backbone.Model.prototype.sync.apply(this, arguments);

ghost/admin/models/themes.js

@@ -3,7 +3,7 @@
     'use strict';
 
     Ghost.Models.Themes = Backbone.Model.extend({
-        url: Ghost.paths.apiRoot + '/themes'
+        url: Ghost.paths.apiRoot + '/themes/'
     });
 
 }());

ghost/admin/router.js

@@ -36,7 +36,7 @@
         blog: function () {
             var posts = new Ghost.Collections.Posts();
             NProgress.start();
-            posts.fetch({ data: { status: 'all', staticPages: 'all'} }).then(function () {
+            posts.fetch({ data: { status: 'all', staticPages: 'all', include: 'author'} }).then(function () {
                 Ghost.currentView = new Ghost.Views.Blog({ el: '#main', collection: posts });
                 NProgress.done();
             });
@@ -63,7 +63,7 @@
             post.urlRoot = Ghost.paths.apiRoot + '/posts';
             if (id) {
                 post.id = id;
-                post.fetch({ data: {status: 'all'}}).then(function () {
+                post.fetch({ data: {status: 'all', include: 'tags'}}).then(function () {
                     Ghost.currentView = new Ghost.Views.Editor({ el: '#main', model: post });
                 });
             } else {