Tooltips in the ContentControl with the Alias of the property being displayed

The aim is to provide a tooltip containing a field's alias when editing content properties - this allows for easy reference when coding up Razor views etc

The tooltip will probably also be useful for other requirements.

I've also re-written the content control's render method as there were a couple of places where attribute and HTML encoding wasn't being performed (e.g. the writer.WriteLine(ex.ToString()); ) which could have allowed injection of HTML into the backoffice.

(I've also removed some empty methods from ContentControl.cs as there was no point in them being there.)