This commit is mainly about the bottom sheet mechanics of showing the toolbar when it is expanded. A place holder layout is used for the bottom sheet content.
When swiping a selected message we remove the selection state at the start and restore it afterwards if the list item isn't removed. Except when the swipe action is "toggle selection". Then we keep the current selection state while the list item is dragged.
If the list is scrolled to the top and items are inserted before the previously first list item, `RecyclerView` is "scrolled" to to show the new first item at the top.
