WIP: Added tinymce editor on course overview

This PR added tinymce editor on overview course in CMS course settings, it includes code plugin in tinymce to allow edit code.
![captura de pantalla de 2014-10-16 14 23 47](https://cloud.githubusercontent.com/assets/31282/4669008/22cb675a-556a-11e4-89a6-e4697b85f193.png)
![captura de pantalla de 2014-10-16 14 23 34](https://cloud.githubusercontent.com/assets/31282/4669015/301137fa-556a-11e4-81bb-a5f466ddf0c8.png)


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