Paginator can now use string or simple arrays for "order

## Problem

The paginator was expecting order with a defined structure :  

    "order" => ["Key" => "DESC", "Key2" => "ASC"]

but ignore order if 

    "order" => "Model.key DESC"
    "order" => ["Model.key DESC", "Model.key ASC"]

## Solution 

Edit the validateSort() from paginator component 
OR 
Consider that the user have to follow the first convention (and ignore this pull request)