[18.0][FIX] document_page: Don't change last history name and summary…

[diggy128]

… when

creating new revision of page.

Fixes an issue where editing a document.page and changing name and/or summary (to create a new revision) also changes name and summary of the history_head.

draft_name and draft_summary are now computed fields (based on history_head) but have set the inverse without actually setting the value, to allow setting them when creating a new draft page.

The issue is prominently evident when using document_page_approval where the name/summary for the new draft also change the last approved version (aka history_head) which should not happen.

[etobella]

Technically makes sense

[pedrobaeza]

But with this, you cannot change the head name and summary...

[etobella]

IT is not working....

If you write only one of the fields, the other are resetted...

[diggy128]

But with this, you cannot change the head name and summary...

In fact you can, because we set inverse on the field (even though not doing anything about it in the inverse method).

If there is a history_head, then these are fetched along with content, otherwise they are kept empty.

This way we always have the correct name and summary from history head, but allows to change them if we change the content

[diggy128]

IT is not working....

If you write only one of the fields, the other are resetted...

That is how I made it work.
When creating a new "version" of a document we should always set a new name and summary describing the changes.
So keeping the same name or summary when the content has changed is wrong.
If I've mistaken something about the usage of these fields let me know and I'll adapt the code.

However, especially in ISO certifications related documentation, having a document history with the same version and / or summary is wrong.
In our internal system, name is used just to increment a version number and summary to describe the changes made.
At some point we could add an analog to Semantic versions to history documents.