Adds more methods to the MembershipHelper, updates the RegisterModel and obsoletes the standard ctor so biz logic is not happening in the model, updates the snippets to use the correct way. Fixes an issue in the membership repo for persisting new members when the member type doesn't contain all the built-in props.

src/Umbraco.Web/Controllers/UmbRegisterController.cs

@@ -24,7 +24,7 @@ namespace Umbraco.Web.Controllers
             MembershipCreateStatus status;
             var member = Membership.CreateUser(model.Username, model.Password, model.Email,
                 //TODO: Support q/a http://issues.umbraco.org/issue/U4-3213
-                "", "", 
+                null, null, 
                 true, out status);
 
             switch (status)