Refactoring MemberService and MembersMembershipProvider from Darrens pull request to fit the changes made the past week.

SecurityHelper is moved to the Umbraco.Web.Security namespace.
MembershipExtensions are changed to the new models
Refactoring the TypedModelBase and UmbracoTempaltePage for the TypedModel POC
Removing the SecurityHelper and moving the 3 methods into the Provider as private classes, as they aren't used anywhere else.

The SecUtility will be removed along with the legacy MembershipProvider when cleanup is possible.
Refactoring the GetById method in the MemberService.
Implementing addtional methods in the MemberService
Adding comments to the MemberService methods