title: Runtime Error on 'Editable' when using Glass.Mapper in Sitecore8.1
body: <p>I have Sitecore8.1 MVC with Glass.Mapper.Sc package (from NuGet) installed. I need to use the 'Editable' method in my cshtml, but I keep getting a runtime error:</p>
  
  <blockquote>
    <p>The name 'Editable' does not exist in the current context</p>
  </blockquote>
  
  <p>Do I need other DLLs, or usings or config updates etc..?</p>