Adding theme switcher to settings/general

closes #488 and #107
- added dropdown for theme selection on general page
- added GET /api/v0.1/themes to retrieve available themes
- modified settings model to get available themes
- modified updateSettignsCache to remove path from settings.activeTheme

ghost/admin/models/settings.js

@@ -4,7 +4,7 @@
 
     // Set the url manually and id to '0' to force PUT requests
     Ghost.Models.Settings = Backbone.Model.extend({
-        url: '/api/v0.1/settings/',
+        url: Ghost.settings.apiRoot + '/settings',
         id: "0",
         defaults: {
             title: 'My Blog',

ghost/admin/models/themes.js

@@ -0,0 +1,9 @@
+/*global window, document, Ghost, $, _, Backbone */
+(function () {
+    "use strict";
+
+    Ghost.Models.Themes = Backbone.Model.extend({
+        url: Ghost.settings.apiRoot + '/themes'
+    });
+
+}());

ghost/admin/tpl/settings/general.hbs

@@ -50,6 +50,15 @@
                 </select>
             </div>
 
+            <div class="form-group">
+                <label for="activeTheme"><strong>Theme</strong></label>
+                <select id="activeTheme" name="general[activeTheme]">
+                    {{#each availableThemes}}
+                        <option value="{{ name }}" {{#if active}}selected{{/if}}>{{ name }}</option>
+                    {{/each}}
+                </select>
+            </div>
+
         </fieldset>
 
         <hr />

ghost/admin/views/settings.js

@@ -41,7 +41,8 @@
 
         showContent: function (id) {
             var self = this,
-                model;
+                model,
+                themes;
 
             Ghost.router.navigate('/settings/' + id);
             Ghost.trigger('urlchange');
@@ -53,9 +54,13 @@
             this.pane = new Settings[id]({ el: '.settings-content'});
 
             if (!this.models.hasOwnProperty(this.pane.options.modelType)) {
+                themes = this.models.Themes = new Ghost.Models.Themes();
                 model = this.models[this.pane.options.modelType] = new Ghost.Models[this.pane.options.modelType]();
-                model.fetch().then(function () {
-                    self.renderPane(model);
+                themes.fetch().then(function () {
+                    model.fetch().then(function () {
+                        model.set({availableThemes: themes.toJSON()});
+                        self.renderPane(model);
+                    });
                 });
             } else {
                 model = this.models[this.pane.options.modelType];
@@ -134,12 +139,13 @@
         },
 
         saveSettings: function () {
+            this.model.unset('availableThemes');
             this.model.save({
                 title: this.$('#blog-title').val(),
                 email: this.$('#email-address').val(),
                 logo: this.$('#logo').attr("src"),
-                icon: this.$('#icon').attr("src")
-
+                icon: this.$('#icon').attr("src"),
+                activeTheme: this.$('#activeTheme').val()
             }, {
                 success: this.saveSuccess,
                 error: this.saveError