larger refactor so we don't need to worry about 'loading' a users groups, it will all just be done, updated queries to fetch a user, it's groups and it's sections all at once, it might be a little heavy but we'll see. Adds/removes a few other methods that didn't seem right and uses group aliases for most things, adds Datbase unique indexes for group aliases and names (need to fix tests though)

src/Umbraco.Core/Models/UserExtensions.cs

@@ -92,7 +92,7 @@ namespace Umbraco.Core.Models
         public static bool IsAdmin(this IUser user)
         {
             if (user == null) throw new ArgumentNullException("user");
-            return user.Groups != null && user.Groups.Any(x => x.Alias == "admin");
+            return user.Groups != null && user.Groups.Any(x => x == Constants.Security.AdminGroupAlias);
         }
     }
 }