Refactoring the legacy base ContentType class to better allow the usage of both new and old api.

A few of the shared properties are now saved by the new api for DocumentType and MediaType, whereas the MemberType still uses the old style.

src/Umbraco.Core/Models/ContentTypeBase.cs

@@ -130,7 +130,7 @@ namespace Umbraco.Core.Models
             get { return _alias; }
             set
             {
-                _alias = value;
+                _alias = value.ToUmbracoAlias(StringAliasCaseType.CamelCase, true);
                 OnPropertyChanged(AliasSelector);
             }
         }