Updated CKEditor to version 4.1.2 (June 2013)

I've used the standard CKEditor plus the following plugins:

- Developer Tools
- Justify
- Preview
- Word Count & Char Count
- Youtube

I also preinstalled the following languages (as these are the ones I use). But you can download the extra languages you need from http://ckeditor.com/:

- English
- Spanish
- Catalan

I also made some changes to `config.js` in order to make dialogs much simple.

In the second commit I pushed some changes I've made in my fork. They're pretty simple and focused on images (I don't know if they could cause any problems for those who upload other content rather than images, someone should review the second commit before merging it.). Basically I added some simple validation on upload and added the option to skip thumbs creation if you don't want the images to be browseable by users. I also changed `django.conf.urls.defaults` to `django.conf.urls` in `urls.py` to avoid warnings in Django >= 1.5

Hope this helps someone else. Thanks! :)