Implement a private/read-only mode #1203
Description
This is a way to protect the privacy of the user.
This is a mode which should not write anything on the storage.
This could be a feature to be activated via the UI, like on any browser.
But we should also consider to maybe force activation via a file on the fs (for portable version) via .private file.
We should also discuss if such a feature should simply forbid to download ZIM files? Or would that be something different, like a "read-only" mode.
Follower of #1166