Datatype should be integrated with Disqus API

[lolautruche]

At the moment, the DisqusComments datatype only checks and sets the open/closed status through the data_int field in the database. This should be done through Disqus API to be fully consistent.

Features needed

• Open/closed status set via Thread API.
  • DisqusCommentsType::fetchObjectAttributeHTTPInput() to set the right status on the content attribute depending on what the user set in the content edit interface
  • DisqusCommentsType::initializeObjectAttribute() to initialize the attribute depending on what is default in the content class
  • DisqusCommentsType::objectAttributeContent() to return the right status
• Check if a thread has content or not
  • DisqusCommentsType::hasObjectAttributeContent()