Added package.js support for themes (and plugins)

Closes #2081
* Amended require-tree to populate availableThemes and availablePlugins to use full file names (`basename.ext`) as keys instead of just basename. This way `image.jpg`, `image.png`, `image.gif` won't overwrite the `image` key.
* Amended require-tree to allow package.json file parsing to return the contents of the file as json on the `package.json` key.
* settings api populates theme data `package` if it exists. Otherwise it assigns `false` to it
* `general.hbs` (salute) was reworked to if there is the package key on the theme is not false, it will use the `name` and `version` keys of that. You can break it by not having a `name` or `version` in the package.json file.
* Added error and warning messages for package.json file parse errors and misses

ghost/admin/tpl/settings/general.hbs

@@ -69,7 +69,8 @@
                 <label for="activeTheme">Theme</label>
                 <select id="activeTheme" name="general[activeTheme]">
                     {{#each availableThemes}}
-                        <option value="{{name}}" {{#if active}}selected{{/if}}>{{name}}</option>
+                        <option value="{{name}}" {{#if active}}selected{{/if}}>{{#if package}}{{package.name}} - {{package.version}}{{else}}{{name}}{{/if}}</option>
+                        {{#unless package}}<script>console.log('Hi! The theme named "{{name}}" does not have a package.json file or it\' malformed. This will be required in the future. For more info, see http://docs.ghost.org/themes/.');</script>{{/unless}}
                     {{/each}}
                 </select>
                 <p>Select a theme for your blog</p>