* Refactor shouldUpdateScroll passing
So far, shouldUpdateScroll has been manually passed down from the very top of
the React component hierarchy even though it is a static function common to
all ScrollContainer instances, so replaced that with a custom class extending
ScrollContainer.
* Generalize “press back to close modal” to any modal and to public pages
* Fix boost confirmation modal closing media modal
* Fix audio and video items in account gallery in web UI
- Fix audio items not using thumbnails
- Fix video items not using custom thumbnails
- Fix video items autoplaying like GIFs
* Change audio and video items in account gallery to autoplay when opened in web UI
* Fix code style issue