Feature/upgrade bootstrap

I have upgraded the bootstrap css and js files from version 2.1.1 to version 2.2.2. I also changed the folder for $this->app_img_folder in the InstallShell.php file. The core bootstrap.css was looking for glyphicons-halflings.png in ../img/glyphicons-halflings.png, which translates to webroot/css/twitter/img, so I have change app_img_folder to be $this->app_img_folder = new Folder(''.CSS.'twitter'.DS.'img', true, 0755) so that the image is found by the css file.