Reimplemented user action to create a category.
Added before filter to categories controller
Changed before filters to use except instead of only.
Changed versions list view not to show versions to which no object corresponds.
Add visible field to Categories, Articles.
Added user functionality to create a single page category.
Some layout changes for users profile articles view.
Fixed single request in categories spec, that was not properly working.
Implemented ordering for categories via the precrusor_id key.