changed links to books to use books/download method

This will allow the files to not be in webroot folder. This commit only changes it for the html views, and not the odps views
changed opds links to use books/download method
created AppModel::getCalibrePath, getCaliberDatabasePath, getDatabaseModifiedTime. This should minimize having to use Configure::read(...)
created ImageHelper::fancybox and ImageHelper::fancyboxJs

applied it to views and indexes
changed ImageHelper::$calibrePath to ImageHelper::getCalibrePath()
added Session component to AppController
added AppModel::getInfo method, and changed xml views to use it