Migrated most of the functionality from RazorLibraryCore to UmbracoHelper and updated RazorLibraryCore to call

the methods in UmbracoHelper so we only have to maintain one set of code. Didn't port over the Wrap methods because
I need feedback on these as to what they do/are supposed to do.
Added the Media methods to UmbracoHelper using the media store stuff.

src/Umbraco.Core/Dynamics/DynamicNull.cs

@@ -11,7 +11,7 @@ namespace Umbraco.Core.Dynamics
     //Because it's IEnumerable, if the user is actually trying @Model.TextPages or similar
     //it will still return an enumerable object (assuming the call actually failed because there were no children of that type)
     //but in .Where, if they use a property that doesn't exist, the lambda will bypass this and return false
-    internal class DynamicNull : DynamicObject, IEnumerable, IHtmlString
+    public class DynamicNull : DynamicObject, IEnumerable, IHtmlString
     {
         public IEnumerator GetEnumerator()
         {