A new upload input and fixes

Great changes on upload input: created a whole new class, using HTML5 api for sending file through XMLHttpRequest. Added progress bar for big files. And fixed error messaging for both inputs (the new, ajax input, and the classic, that uses iframe) (Fixes #1).

Added a CakeSchema for JjMedia.

Changed the BuroOfficeBoyHelper::addHtmlEmbScript() so it works when called at the layout file (outside the view).

Also, a small change on CsContentStreamHolderBehavior that fixes a non documented bug (now the script works even when the primary key is forced on data to be saved for the first time.