Moodle forum: Add not deletable editing information to a post

In MDL-35788, the timestamp of a post will be fixed to its original creation date.

However, even with this patch, a user can edit the post and the the other forum members do not even get a hint - so all changes are so to say done secretly.
For UX reasons and transparency, it is essentially necessary that the users get to know if and when a post was edited in the meantime.

To achieve this, there are some options:

• Only state that the post was edited and when - like this example:
• State how often the post was edited and when the latest action was.
  For example: edited 3 times, last modified on Wednesday 11 July 2018, 3:50 PM
• Combine either of these possibilities with the naming of the author who did the modification - especially if a person who is not the author do the changes.

The changes can or maybe even should be printed at the footnote of a post - the example here in the heading is just for illustrational purposes.

Currently, some of the information proposed here are added to the text editor:

However this line is deletable and if the editor does delete it, the changes will be not obvious for other users. Also to separate user content from system information, we would prefer to add this information to the header or footer area of the post.

Best, Kathrin