Fiduswriter

**Fixes:**
* Prevent images from being lost when upgrading a document from previous fidus writer version
* remove empty text nodes from comments and documents
* fix link to maintenance page in warning message

**Fixes:**
* Better response to document deletion when document is part of a book
* Make the email confirm page work on slightly older browsers

**Fixes:**
* document management script
* overview page menus

**Features:**
* Margin box filter
* Editor design updates


**Changes:**
* Replace `let` with `const` in editor code where applicable
* Rename "is Major" to "high priority" user facing.

**Fixes:**
* Margin box placement fixes
* Footnote numbering fixes
* Allow track marks in title/subtitle

**Features:**
* Add plugin hook to the global JavaScript "app" (applies to all pages beyond login)
* Add "scroll" option to dialogs in case their content should be scrollable


**Changes:**
* Reuse user info object on all pages
* Use vivliostyle-print instead of VIvliostyle.js directly

**Fixes:**
* Various fixes related to navigating away from the editor page
* Some let => const conversions
* In export `sectionfnlist` => `section.fnlist` to allow using it in exporters for multiple documents.

**Fixes:**

* Table sorting on overview pages.