Add text format info to enable alternate formatting

[ywarnier]

In Chamilo, some elements are stored in HTML in the database. Markdown (and some others) are becoming popular alternatives to HTML. Easier to write and understand. Enabling teachers to write/import/export their course introductions, documents, questions, etc in alternative formats would be great, but it requires Chamilo to know in which format it is stored initially, so as to maintain this format (which each teacher may have other feelings about, so it cannot be a general platform setting).

To enable this, we would first need a field, in the database, specifying the format in which it is stored. As such, I suggest modifying the resource_node table in Chamilo 2.0 to add a resource_format_id field which would be defined in a new resource_format table. The first format available there would be "txt" and apply to normal text fields. The second format would be "HTML" and apply to all database fields that have a WYSIWYG editor attached to them.

Then (later on) additional support can be added for other formats.