QTI: use document editor in file upload question type

The extent to which OnlyOffice could be used for direct editing must be evaluated. 

The asynchronous behaviour of the save action in OnlyOffice cannot guarantee that the content has actually already been transferred to OpenOlat when the OnlyOffice window is closed.

If a solution can be found for this, the use of the editor is also supported in the test.

After further investigation and discussions with the client we decided to stop the development on this issue for the moment: 

• OpenOlat has no way to force saving and to quit the document editor. With enough code this could be implemented by closing the editor window / iframe, however at this time there is no link between the test and the editor controller.
• In any case, the timing can not be guaranteed to be exact to the second. The editor needs to convert the document and save it on the OpenOlat server
• There are many difficult scenarios when the editor must be closed server-side: when the test item time is up, when the test time is up, when the coach pulled the tests etc. It is unclear how this can be implemented UX-wise so that users understand what happens, e.g. how to display a timer in the document editor
• When this feature is implemented, authors are going to use it. They are not aware of the technical impact, requirements and licenses involved. What happens when test with 1000 user users the document editor but only 500 licenses are available and shared across all authors? Such a situation is not planable or foreseeable by admins. 
• The dependency to external server create an additional risk in an exam setting that is difficult to communicate to the authors. They have the great feature to use the document editor to write essays, they will use it and will not be aware that by doing this the exam depends on the availability of the document editor server which is under control of unknown other people.