Add 'column' field to TemplateColumn context

A small change to add a 'column' field to the context that is passed to templates rendered by TemplateColumn.  This allows for reusable column templates like this (for use making columns editable via js library):
{code}
<span class="editable" data-col="{{column}}" data-id="{{record.id}}">{{value}}</span>
{code}