Enable to set formatter and editor on the same cell

This enhancement makes possible to use formatter on editable cell too. 
In previous implementation it was impossible, because when formatter was set on cell, renderCell method was always ignored. 

In this enhancement we moved formatter resolving into our defaultRenderCell method.
This method is being called from Grid's renderRow and also from Editor's renderCell method, when Editor has property editOn set to "click" or "dblclick".