Added links to revert version.
Implement controller behaviour for reverting article versions.
Implemented behaviour to move a category behind another.
Changed versions revert icon to step-backwards arrow
Changed single page category requests to not redirect and also display a category edit link.
Changed category edit links to only appear when signed in.
Refactored header layout to use all_in_succession function for category retrieval.
Changed visibility editing behaviour to change a categories visibility according to its articles if it is a single page category.
Changed icon for category editing to a list-like icon.
Added layout for invisible articles.