Add expander signal

[Aphexus]

In Kiwix JS and the wikipedia zim when clicking on a section (such as Examples) it hides the content but there is no way of knowing it does this or not since everything looks the same. [One might be able to tell that the next line is that of a new section but it is not so obvious]

E.g., having a simple expander indication like a down arrow or when unexpanded some text that says "expand" would be helpful.

[Jaifroid]

Thank you for this report @Aphexus. I think currently the opening and closing of sections is in transition, and is no longer supported in the newest ZIMs scraped with the dev version of mwOffliner. In reality, I think this issue belongs to mwOffliner, because we don't do anything in Kiwix JS to add code that is not already in the ZIM, so this would only be fixable upstream, not here. However, I'm not sure it's worth transferring this issue to mwOffliner because a recent issue there about headings no longer being closeable was concluded with the fact that this functionality will no longer be supported going forward.

It strikes me that you might be using the PWA version of Kiwix JS, rather than the Browser Extension version (this Repo). However, even there, we depend on upstream support for the feature, and although we tried to emulate it in Restricted mode (former "jQuery mode"), we need to await finalization of the ZIM format for ZIMs scraped from the mobile-html endpoint to decide what to do about this functionality. If it is no longer supported anywhere in Kiwix, it may be best just to remove it.

EDIT: I'll leave this open until we have certainty upstream.