U4-2417: show media picker image as link to the original image.

Order of the views in the markup did not match the order of the Style enum.
ImageViewer control now selects the view by matching the ViewerStyle enum to a View ID. This way the order of the views in the markup is no longer important.

Also:
Removed user control from Umbraco.Web project, moved designer code and added code behind class for user control to Umbraco.Web.UI
Refactored code to use Umbraco.Core.IO
Removed some code that was commented out
Merge pull request #46 from michielvoo/u4-2417

U4-2417 Could the preview thumbnail link to the full image