Fixes some issues with the User membership provider, updates user create dialog to also have an email address (which is required by membership), adds validation to the member and user create dialogs to ensure that the email address is validated to be a correcty formatted address.

src/Umbraco.Core/Security/MembershipProviderBase.cs

@@ -605,7 +605,7 @@ namespace Umbraco.Core.Security
             return pass;
         }
 
-        protected bool IsEmailValid(string email)
+        internal static bool IsEmailValid(string email)
         {
             const string pattern = @"^(?!\.)(""([^""\r\\]|\\[""\r\\])*""|"
                                    + @"([-a-z0-9!#$%&'*+/=?^_`{|}~]|(?<!\.)\.)*)(?<!\.)"