added replace claim functionality. fixes #232

 - added ReplaceClaimAsync method to IUserClaimStore interface
 - implemented ReplaceClaimAsync method from IUserClaimStore inside the
   Microsoft.AspNet.Identity.EntityFramework.UserStore<TUser, TRole,
   TContext, TKey>
 - added ReplaceClaimAsync method to UserManager
 - added UserManager tests for ReplaceClaimAsync method.
 - added some UserStore tests for ReplaceClaimAsync implementation of
   IUserClaimStore
Rename parameter of IUserStore.SetNormalizedUserNameAsync method

Fixes https://github.com/aspnet/Identity/issues/244
Allow the application developer to specify the iteration count for membership passwords.
Updating to release NuGet.config
Merge branch 'release' into dev
Updating to release NuGet.config
Merge branch 'release' into dev
Fixing dev NuGet.config