removve chapter management header from chapter preview pages; remove/rewrite some buttons to make chapter->preview draft->edit flow clearer
change sentence case button text to title case
changes after Elz's review: setflash instead of flash and ts()
change ts string to remove key and default
tidying & null ref aversion for flash message on deleting a chapter
code review changes: spacing around conditionally added html classes, wrap confrirm messages in ts
clarify flash message re: chapter drafts in work drafts, and move it to a helper method